About the 8th Biennial Workshop on OMVPE: Technical Program, Wednesday Afternoon Sessions (April 16)

The following papers will be presented at the 8th Biennial Workshop on OMVPE, on Wednesday evening, April 16th, 1997. The calendar of events describes the entire technical program.

SESSION IX: POSTER SESSION

5:00 pm to 7:00 pm: Poster Presentations Viewing

Effect of Substrate Misorientation and Growth Temperature on the Morphology of CdTe Deposited by Organometallic Vapor Phase Epitaxy: Kijung Yong, Paul J. Sides, and Andrew Gellman, Dept. of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213

A dramatic demonstration of the interplay of substrate misorientation and film quality will be presented. The effects of substrate misorientation and growth temperature on CdTe epilayers homoepitaxially grown by OMVPE were investigated with CdTe(100) and CdTe(100) substrates misoriented by 2, 4, 6, and 8 degrees toward (111)Te in the growth temperature ranging from 337 degrees C to 425 degrees C. The number density of the well-known pyramidal facets that form on CdTe (100) decreased to zero with increasing misorientation angle up to 4 degrees. At higher misorientation angles, film morphology deteriorated and triangular protrusions, like fish scales, appeared on the surface. The size of hillocks decreased but the density of hillocks increased with increasing temperature. A remarkable improvement of morphology with increasing temperature was observed at higher misorientations. A cross-sectional TEM image showed that the CdTe mirrorlike films at 4 degrees were epitaxial single crystals with no planar defects.

Study of Atomic Layer Epitaxy for II-VI Material Growth with Organometallic Molecules: Yi Luo, David Slater, Ming Han, Joseph Moryl, and Richard M. Osgood, Jr., Columbia Radiation Laboratory, Columbia University, NY 10027

We present a study of ALE for the heteroepitaxy of IIVI semiconductors using organometallic molecules in a binary reaction sequence. The study focuses on understanding both the fundamental surface reaction and materials for growth on the first 10 bi-layers. Dimethylcadmium and hydrogen sulfide are employed as precursors for the growth of a model system of CdS on a ZnSe(100) substrate exhibiting a well ordered c(2x2) reconstruction. The alternate supply of source molecules to the growth surface is found to result in self-terminating growth of both Cd and S layers during each cycle of the binary reaction sequence. A primary consideration in this study is to achieve growth at the lowest possible temperature in order to reduce material interdiffusion and to eliminate carbon incorporation by minimizing any possible hydrocarbon dissociation. The grown layer was characterized using AES, XPS, LEIS and LEED at different stages of the process. The data shows well ordered stoichiometric layer-by-layer growth has been achieved at room temperature.

The Growth of CdS Nanocrystallites in the SiO 2 Molecular Sieve: Guangyou Yu, Xiwu Fan, Dezheng Shen, Baojun Yang, and Jiying Zhang, Laboratory of Excited State Processes, Changchun Institute of Physics, Chinese Academy of Sciences, Changchun 130021, China

At present, intensive research work is going on the nanometer-sized semiconductor material because of the quantum-confined effect. The preparation of this kind of material often use chemical synthesis methods such as colloidal suspensions. These methods usually meet the main difficulty, i.e. dispersion in the size of the crystallites. This dispersion originates from several mechanisms such as coalescence and decomposition of particles with time and high temperature. In order to avoid the effect of desperation in the size, the CdS nanocrystallites were grown in SiO2 molecular sieve by "intrazeolite topotaxy" method for the first time. Photoluminescence of the CdS nanocrystallites fabricated in SiO2 molecular sieve was observed at 77K excited by N2 laser. All samples showed one emission peak. The position and line width of the peak changed with differed growth time, which showed the growth process of CdS nanocrystallites in molecular sieve. Due to weak confinement, blue shift of the emission peak is not large compared to CdS bulk, but line width is narrowed obviously.

The Use of Atmospheric Pressure MOVPE for the Growth of High Performance Uncooled 1300 nm DFB Laser: A.J. Taylor, A. Bridges, R.H. Moss, and W.S. Ring, Hewlett Packard Ltd., White House Rd., Ipswich, Suffolk, IP1 5PB, UK

Modern telecommunications requires low cost high speed lasers operating over a wide temperature range. The manufacturing challenge from a materials aspect is obtaining good uniformity and high precision in a complex, strained layer laser structure. The target wavelength window is 10nm in order to optimise the position of the gain peak with respect to the grating wavelength, to achieve full temperature operation. Many companies have opted for reduced pressure MOVPE. We have concentrated on the use of atmospheric pressure MOVPE, which has the advantages of less complicated equipment and more efficient use of source materials. The material was grown in a horizontal Thomas Swan MOVPE reactor, without substrate rotation and using standard sources. The BH strained quantum well laser has an active region consisting of 7 compressively strained (+0.8%) quantum wells with 1100nm quaternary barriers. Material has been assessed using XRD, PL, electrochemical profiling, TEM and SIMS. Good wavelength uniformity has been obtained, with the best wavelength spread across a 28x28mm centre square of a 2" InP wafer being as low as 3 nm. BH DFBs made this way operate single mode from -40°C to + 85°C and we have obtained the world's lowest threshold of 26mA at 85°C. Results on the growth of the structures and device results will be presented.

1.55 µm Lasers using Separate Strain Compensation Heterostructure: P. Abraham, A.L. Holmes, M.E. Heimbuch, G. Fish, S.P. Den Baars, and J.E. Bowers, Electrical and Computer Engineering Dept., University of California, Santa Barbara, CA 93106-9560

The InGaAsP/InP system suffers from two major problems for the growth of high-strain-quantum-well-laser structures. Its miscibility gap prevents the growth of high-energy, high-tensile-strain barriers and its low conduction-band-offset causes active region carrier leakage at high temperature. We compensated the strain of the quantum-wells outside of the active region with In1-zGazP. This allows us to choose the barrier band gap energy without restriction due to the miscibility gap. Moreover, because the conduction band offset between InP and InGaP (DEC=EC(Inl-zGazP) EC(InP)) is positive and the InP/ Inl-zGazP lineup is of type II, the In1-zGazP layers reduce the active region electron leakage but does not introduce a barrier for the holes to reach the QW. The X-ray spectra of such structures show that up to six 90 è thick 1.2% compressive strain QW can be grown with only 0.13 % tensile strain barriers without relaxation and with good cristallographic quality. The preliminary results on broad area lasers show a threshold current density in the active region of 39 A/cm2 per quantum-well for infinite cavity length. X Ray spectrum of the structure shown in the inset. The peaks labeled -2 to 2 are the zero order and satellite peaks of the active region (QW+barriers). The enlargement of the InGaP peak clearly shows satellite peaks due to the spacing between the two InGaP layers.

Selective MOCVD of Catalysts on Micromachined Calorimetric Gas Sensors: Ronald P. Manginell, James H. Smith, Antonio J. Ricco, Daniel J. Moreno, and Robert C. Hughes, Sandia National Laboratories, Albuquerque, NM 87185-1080, Robert J. Huber, University of Utah, Salt Lake City, UT 84112

Micro-Chemical Vapor Deposition ("microCVD") of catalytic films on surface-micromachined microfilaments has been investigated. Atmospheric-pressure deposition of Platinum and Palladium on microfilaments is accomplished by thermal decomposition of acetylacetonate-based precursors of those metals; deposition occurs selectively only on those filaments that are electrically heated. Catalyst morphology, characterized by scanning electron microscopy, has been modified by altering deposition time, filament temperature and through the use of pulsed heating of the filament during deposition. The metal catalyst morphology plays an important role in the sensitivity of these devices when used as combustible gas detectors. Currently, methods of in-situ growth monitoring are being investigated. These efforts rely on the fact that the thermal time constant of a filament with catalytic metal is measurably greater than one without. Results obtained by pulsed heating of filaments prior, and subsequent to metal deposition reveal that the thermal lag due to catalytic metal is, to first order, proportional to the film thickness.

Characterization of Initial InAs Epilayers Grown on InP Substrates by MOCVD: Jwayeon Kim, Dept. of Materials Science & Engineering, Ho Seo University, San 29-1, Sechul-ri, Baebang-myoun, Asan, Chungnam, 336-795, Korea

The properties of InAs epitaxial films grown on (001) InP substrates (oriented 2° off (001) toward [110] direction) using metal organic chemical vapor deposition (MOCVD) are reported. Transmission electron microscopy (TEM) techniques were used for this study. Films of 170 Å thickness grown at 405°C showed three kinds of misfit dislocation arrays such as, a straight orthogonal array along <110>, an array along <100>, and an array of dislocations tilted a few degrees from the [ll0] direction. Upon annealing the 600 Å, 1,400 Å, and 2,000 Å InAs films at 600°C most misfit dislocations became Lomer type oriented exactly along <110> directions irrespective of the two degree angle tilt. The misfit dislocation spacing were inversely proportional to the InAs thickness. And the residual elastic strain was approximately ~0.0095 (30%) in the 1,400 Å InAs film grown at 405°C without annealing. These phenomena was interpreted to the relationship between the dislocation interaction energy among parallel misfit dislocations and opposite InAs epilayer strain energy generated from dislocation interaction energy. Threading dislocation density generated by island coalescence in InAs film (2,000 Å) grown at 480°C was ~1.7 x 1010/cm2 even after annealing at 660°C or higher temperature.

Effects of Thermally Grown Native Oxides on the Luminescence Properties of MOCVD-Grown Heterostructures: R.D. Dupuis, B.P. Tinkham, and M.R. Islam, Microelectronics Research Center, The University of Texas at Austin, Austin TX 78712-1100, A.P. Curtis and G.E. Stillman, Center for Compound Semiconductor Microelectronics, University of Illinois at Urbana-Champaign, Urbana IL 61801-2991, and R. Hull, Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 2903-2442

Data are presented on the characteristics of GaAs and InGaP layers adjacent to native-oxide regions derive from epitaxial AlGaAs and InAlP films grown by metalorganic chemical vapor deposition. The optical properties of the heterostructures has been studied using 300K and 4K photoluminescence (PL) and 300K time-resolved PL. Impurity concentrations have been analyzed using STMS and the structural characteristics have been studied using transmission electron microscopy analysis. The luminescence intensity and lifetime from GaAs "active regions" drop dramatically when the adjacent AlGaAs "window layer" is oxidized completely. However, there is an increase in the PL efficiency and decay time of the luminiscence with the oxidation of InAlP window layers. Furthermore, there is a marked change in the impurity-related luminscence in the 4K PL spectra of the GaAs layers after oxidation, indicating a change in the BULK properties of the GaAs layer. The PL intensity and the TRPL lifetime for InAlP/InGaP quantum-wells and thick double heterostructure (DH) active regions also increased for oxidized samples. These results have important implications for devices, including vertical-cavity surface-emitting lasers and LED's.

LP-MOVPE Growth of (Al)GaInP using H 2 or N 2 as the Carrier Gas: A Comparison: H. Hardtdegen, Th. Korst, R. Schmidt, U. Breuer, and D. Schmitz1 , Institute of Thin Film and Ion Technology, Research Center Juelich, D-52425, Juelich, FRG, 1 Aixtron Semiconductor Technologies GmbH, Kackertstr 15 -17, D-52072, Aachen, FRG

GaInP/AlGaInP heterostructures are of great interest for high brightness light emitting diodes (HBLEDs). Industrially, the deposition of these structures is performed by MOVPE due to the large quantities of HBLEDs needed. Enormous amounts of highly explosive hydrogen carrier gas as well as PH3 are consumed during deposition. The replacement of hydrogen for nitrogen as the carrier gas has been shown to increase the process safety whilst reducing the hydride consumption in other material systems [1-5]. In this contribution we will present -a comparative investigation of the influence of the carrier gases nitrogen and hydrogen on the structural and optical characteristics of (Al)GaInP. The effect of the carrier gas on the ordering of the group III elements on the respective sublattice will be discussed.

Purification of TBA for the MOVPE of (AlGa)As: M.F. Robinson, J.E. Dixon, EMF Ltd., Wentworth Ely, Cambridgeshire CB6 3 QE, UK, A. Salzmann, A. Greiling, SGS Mochem Products GmbH, D-35041 Marburg, Germany, S. Leu, W. Stolz, Materials Sciences Center, Philipps-University, D-35032 Marburg, Germany

The interest of using liquid organic group-V-sources as substitutes for the highly toxic hydride gases (AsH3, PH3) for metal organic vapour phase epitaxy (MOVPE) and metal organic molecular beam epitaxy (MOMBE) is increasing drastically in recent years. These novel sources like tertiarybutyl-arsine (TBA) and -phosphine (TBP) offer some crucial advantages, i.e. reduced vapour pressure, enhanced cracking efficiency, reduced amounts of waste material, reduced toxicity and, thus, a significant improvement in the overall safety for the entire epitaxial growth processes. While device-quality epitaxial layers have been demonstrated for various Al-free III/V-semiconductor systems using these compounds, still severe problems exist with respect to the incorporation of oxygen-related deep centers in Al-containing layers ((AlGa)As, (AlGaIn)P). Therefore, different purifications steps including the DEOX' -technology have been applied to significantly reduce the residual oxygen level in TBA. The influence of the different purification steps on the (AlGa)As epitaxial layer quality grown in combination with both trimethylaluminum (TMAl) as well as the novel dimethylethylamine-alane (DMEAAl) is presented and discussed in relation to the necessary reduction of deep centers for the application of TBA in the growth of Al-containing device structures.

MOVPE Growth of InPSb/InAs-Heterostructures for the Mid Infrared Emitters: M. Heuken, C. von Eichel-Streiber, A. Behres, B. Schineller, K. Heime, C. Mendorf *, H. Lakner *, E. Kubalek *, Institut fur Halbleitertechnik, RWTH Aachen, Templergraben 55, D-52056, Aachen, * Gerhard Mercator Universitat Duisberg, Bismarckstrasse 84, 47048 Duisberg

The low pressure MOVPE growth of InPSb/InAs heterostructures was investigated in order to optimize mid infrared light emitting devices. High resolution X-ray diffraction, photoluminescence at 10 K electrical measurements and scanning transmission electron microscopy (STEM) was carried out to optimize the growth conditions. Despite the predicted miscibility gap of InPSb sharp X-ray peaks of 43.3 are sec were observed from nearly lattice matched layers. Layers with large mismatch to the InAs substrate ( a/a > 2000ppm) show broad X-ray peaks with a FWHM >250 arc sec. PL measurement at 10 K show a broad peak (FWHM 50 - 70 meV) with a low energy tail which is nearly independent of excitation density. zcontrast and bright field images of these mismatched layers reveal contrast variations. The effect of dopant incorporation (H2S for e-type, DEZn for p-type conduction) was investigated in InPSb/InAs pn diodes.

Anisotropic and Isotropic Growth of Three Dimensional Islands of GaInAsSb Epilayer by Metalorganic Chemical Vapor Deposition: Shuwei Li, Yixin Jin, Baolin Zhang, Yongqiang Ning, Tianming Zhou, Hong Jiang, Guang Yuan, and Yuan Tian, Changchun Institute of Physics, Chinese Academy of Sciences, 130021, Changchun, China

The quaternary GaInAsSb alloys are the most promising candidate materials for use in infrared detectors of room temperature operation. The alloys with direct band gaps adjustable between 1.7 and 4.3 mm can be grown lattice-matched on GaSb,InP, and InAs substrates. During the growth of GaInAsSb epilayers by MOCVD, at the critical thickness the accumulated strain energy imposes the equilibrium situation to form 3D islands which are surrounded with the facets. In certain range of thermodynamic, the growth rates of the facets are strongly affected by differently oriented surfaces. When the growth rate of the higher index orientation is larger, the 3D island growth is anisotropic mode and forms finally pyramidal hillock which was observed in a image of Atomic Force Microscopy (AFM). On the other hand, the growth rate is not sensitive to the directions of facet planes. When growth rate of growth nucleus is larger than growth rate of the highest index plane, the growth of 3D island displays isotropic growth mode and forms finally smooth and perfect 3D island which was observed AFM image, too.

An Integrated Approach to the Handling of Phosphorus-Based Byproducts Generated in MOCVD Reactors: Alan G. Thompson, P. Zawadzki, P. Fabiano, and R.A. Stall, Emcore Corp., 394 Elizabeth Ave., Somerset, NJ 08873

Many optoelectronic devices, such as high-brightness LEDs, laser diodes, and solar cells are now being produced in large volumes. The handling of phosphorus-based byproducts from MOCVD reactors has been problematical, and has been exacerbated by the trend toward large scale reactors. The pyrophoric forms of elemental pbosphorus and unreacted hydrides must be safely trapped for safety and environmental reasons. We report here an integrated approach to this problem that concentrates on efficiently collecting all byproducts at traps that can be safely and easily cleaned. This approach includes reactor and exhaust designs that preclude phosphorus deposition, a water cooled phosphorus trap, an exhaust gas abatement system that traps unreacted hydrides to below IDLH levels, and appropriate vacuum pumps. In particular, we discuss a cleaning technique for the phosphorus trap that avoids exposure to air, and the relative merits of dry and oil filled vacuum pumps. Long term results from a large reactor (38 x 2" wafers/run) running three shifts will be presented proving the efficacy of this approach.

Growth of High Quality InGaN based MQW Structures in a Production Scale MOCVD Reactor: Mathew J. Schurman, Chuong Tran, Tom Salagaj, Robert F. Karlicek Jr., and R.A. Stall, Emcore Corp., Somerset, NJ

We have grown several high quality multiple quantum wells based on InGaN in a multi-wafer rotating disc MOCVD reactor. X-ray diffraction measurements show superlattice fringes arising from the MQW structure, indicating a high structural quality. Photoluminescence (PL) peaks have been obtained in the range from 390nm 480nm with a typical full-with at half max of 25nm. The influence of such parameters as well thickness and composition have been found to effect the width and intensity of the photoluminescence peak and this relationship will be discussed. The influence of the barrier width and composition on the PL will also be discussed. The high degree of wavelength uniformity exhibited by these layers indicates the excellent control over well/barrier composition and widths for 2" substrates.

Growth and Tracking Issues Associated with Production Processes in a Multi-MOCVD Reactor Environment: Michael N. Cleroux, Cornelis Blaauw, and Norbert Puetz, Nortel Technology, PO Box 3511, Station C, Ottawa, ON, Canada, K1Y 4H7

The fabrication of opto-electronic devices using epitaxially grown structures of III-V compound semi-conductors in a production environment requires stable, controlled process steps. In addition, tracability of product flow is a mandatory requirement for IS0 9000 certification. Nortel's Ottawa-based MOCVD facility includes several epi-reactors, some of which are used to grow identical, InP-based emitter structures. Most devices consist of structures which require multiple epitaxial growth steps for their fabrication. When each growth step of a multi-growth structure can be carried out in more than one reactor, the number of possible product flow paths increases dramatically. Ensuring tracability of the product flow and consistency of the material quality requires stringent monitoring and verification procedures. We have developed a tracking system for the growth and analysis associated with the process flow of the fabrication of III-V opto-electronic emitters, using a commercially available relational database. The system provides an on-going record of all important aspects of the epitaxial growth process from the initial request for growth of a particular structure and identification of the substrate used, through all intermediate growth and analysis steps. To delivery of the fully grown structure to the processing area. It also allows convenient translation of data into statistical process control charts. Problems and challenges encountered in creating the database structure and in scaling up from a single epi-reactor to multiple MOCVD reactors will be presented and discussed.

Al-Ga-In Nitride Heterostructures: MOVPE Growth in Production Reactors and Characterization: R. Beccard, O. Schoen, B. Wachtendorf, D. Schmitz, and H. Juergensen, Aixtron GmbH, Kackertstrasse 15-17, D-52072 Aachen, Germany, and E. Woelk, Aixtron Inc., 1569 Barclay Blvd. Buffalo Grove, IL 60089, USA

Various AlGa-ln-Nitride alloys have been grown in MOVPE Reactors with load capacities between 1x2" and 7x2" (AIXTRON Planetary Reactors"). GaN as a base material is grown with an excellent optical quality and very good thickness uniformity Thickness variation is in the percent range on one 2" wafer. GaInN with PL emission wavelengths in the visible blue regime have also been produced with an outstanding compositional uniformity GaInN wavelength uniformities better than 1 nm on a 2" wafer have been achieved. Finally, Al(Ga)N is demonstrated as the material with the widest bandgap. The fabrication of heterostructures from these binary and ternary materials is also described. The choice of suited growth processes, especially the optimum growth temperatures, is discussed. Characterizations of the heterostructures by photoluminescence, x-ray diffracation and sheet resistivity measurements are also presented. Furthermore, we will present data on doped material. The results show that a class of production-scale MOVPE reactors is available allowing a reliable and efficient production of Al-Ga-ln-Nitride based optoelectronic devices.

In Situ Monitoring and Control for MOCVD Growth of AlGaAs and InGaAs: A. Kussmaul, P.C. Colter, R. Sudharsanan, A. Mastrovito, N.H. Karam, Spire Corp., 1 Patriots Park, Bedford, MA 01730-2396; S.C. Warnick, M.A. Dahleh, Dept. of Electrical Engineering and Computer Science, MIT, Cambridge, MA 02139

We have used spectroscopic ellipsometry to perform real-time monitoring during MOCVD growth of AlGaAs (on GaAs) and InGaAs (on GaAs and InP). Optical constants for these materials were obtained at growth temperatures of 600-700C. This information permits real-time extraction of composition and layer thickness from the raw ellipsometric data at sample rates on the order of 0.5 Hz. We demonstrated closed-loop control of composition, growth rate, and total layer thickness on AlGaAs-based structures, including Bragg reflectors. More work is required to allow reliable extraction of composition and thickness in view of substrate wobble and thickness non-uniformities. It is, however, already clear that spectroscopic ellipsometry is an extremely powerful monitoring and quality-control tool, giving important real-time information on complex structures that would be difficult and time-consuming to obtain after growth. We will give specific examples for quantum well structures and Bragg reflectors.

A Resonant Acoustic Composition Analyzer for the Continuous in-line Monitoring of Low Pressure MOVPE Processes: A. Wajid, C. Gogol, C. Hurd, M. Hetzel, and A. Spina, Leybold Inficon, 2 Technology Place, East Syracuse, NY 13057

We describe a very sensitive resonant acoustic binary gas composition analyzer, optimized for inline monitoring of the precursor gases used in MOVPE processes. This compact (18 cc) stainless steel sensor is temperature stabilized and has fast response to process variations. It has been successfully operated at line pressures from atmosphere down to 50 Torr with gas flow rates of up to 1800 sccm. Long term stability, reproducibility and sensitivity are established in absolute terms, corroborated by laboratory and process data. Measurements of the dynamic response characteristics of TMI bubblier lines at low pressure are presented. Factors limiting the accuracy and reproducibility of the device are also detailed. The instrument may be utilized for closed loop control of the delivery of any of the Metallorganic materials with hydrogen, nitrogen or argon carrier gases. Altematively, it may also be used as a diagnostic tool to verify system performance.

Ultraviolet Absorption Sensors for High-Temperature Superconductor MOCVD Precursors: William J. DeSisto and Brian J. Rappoli, US Naval Research Laboratory, Washington, DC 20375-5347

In MOCVD of HTS materials, precursor concentration variation results in uncontrolled film growth. Ultraviolet absorption spectroscopy can be used to measure precursor concentrations in-situ, providing a useful tool in feedback control application. A MOCVD reactor was modified to incorporate high temperature UV gas cells located between the respective precursor bubblers and mixing manifold. Fiber optic cable was used to couple the cells to the light source and detectors. Light intensity was measured from each cell with a dedicated spectrograph/photodiode array in dual beam mode. UV spectra were collected for Ba4(thd)8, Y(thd)3 and Cu(thd)2 at intervals of less than one second. Absorption values, at magnum wavelength, for Y(thd)3 and Cu(thd)2 stabilize after approximately 15 minutes of bubbler purging. Cu(thd)2 shows a small increase in absorption during film growth while the Y(thd)3 exhibits relatively stable gas phase concentration. The barium compound showed a marked decrease in absorption during film growth. The change in gas phase Ba4(thd)8 concentration is consistent with the unstable nature of this compound.

Ligand Exchange Reactions in Organometallic Vapor-Phase Epitaxy: Menno Kappers, Kerri Wilkerson and Robert Hicks, Chemical Engineering Dept., 5531 Boelter Hall, University of California, Los Angeles, CA 90095-1592

The organometallic vapor-phase epitaxy (OMVPE) of Cd1-xZnxTe using diethylziinc (DEZn), dimethylcadmium (DMCd) and diisopropyltellunde (DiPTe) has been monitored in real time by gas-phase infrared spectroscopy. Each organometallic compound exhibits characteristic C-H bending and M-C stretching modes between 750 and 450 cm-1. The infrared data reveal that DMCd and DEZn exchange their alkyl ligands in the feed lines to the reactor, forming MECd, DECd, MEZn and DMZn. The decomposition rates of these precursors vary over a wide range with DECd reacting at ~250°C 1ower temperature than DMZn. This makes it difficult to deposit an alloy of uniform composition. Under most conditions, Cd-rich films are deposited near the reactor inlet, while Zn-rich films are deposited further downstream. However, a narrow process window exists whereby alloys containing small amounts of zinc are uniformly deposited over the substrate. The dependence of the alloy composition and deposition profile on the process conditions will be discussed at the meeting. We also hope to present some results on ligand exchange reactions during IIIV OMVPE.

Investigations on Low-Temperature OMVPE Growth of InGaAs/InP using Alternative Sources (TBAs, TBP): M. Czub, W. Strupinski, M. Wojcik, J. Gaca, B. Surma, Institute of Electronic Matrials Technology, ul. Wolczynska 133, 00-919 Warsaw, Poland

Growth of high quality InP and InGaAs using the less hazardous liquid group V precursors, TBAs and TBP has been achieved. Besides the safety advantages of the liquid sources, the lower pyrolysis temperatures of these materials have several technical advantages. The growth temperature can be reduced which minimizes the intermixing and the doping inter- diffusion effects at the heterointerface. Another advantage is the reducing V/III ratio in comparison to arsine and phosphine which results in lower material consumption and lower waste handling costs. A systematic study compares the quality of InP and InGaAs epitaxial layers grown by low-pressure organometallic vapour phase epitaxy (OMVPE) using TMG and TEG trimethylindium (TMIn), phosphine (PH3), arsine (AsH3) and tertriarybutylophosphine (TBP) and tertriarybutylarsine (TBAs) sources. High quality InP layers are obtained with both phosphorus sources for growth at high V/III ratio. High quality InP and InGaAs layers can be grown at a lower V/III ratio and at low temperatures with the TBP, TBAs sources than with the phospine and arsine sources. The 77K mobility of InGaAs lattice matched to InP (grown with TBAs) was 72 360cm2/Vs for n=1.5x1015cm-3 and thickness of 2mm. Excellent morphologies are obtained for the growth of InP between 530 and 590°C for TBP. V/III ratio as low as 1.3 have been used to grow InP epilayers with featureless morphologies at 600°C. The highest mobility at 77K were: 160000cm2/Vs (using PH3) and 120000cm2/Vs (using TBP). TEGa was also applied as a galliurn source because of lower decomposition temperature Thus, the lower growth temperature is possible comparing to TMGa. The promising results allow to apply TEGa for low temperature GaInAs growth (below 600°C) and to develop device structures.

Role of High Energy Photons in Dual Spectral Source Rapid Isothermal CVD: Y. Chen, R. Singh, and R. Sharangapani, Dept. of Electrical and Computer Engineering, Clemson University, Clemson, SC 29634-0915

The use of tungsten halogen lamps and the deuterium lamp as the sources of thermal and optical energies has been exploited to deposit high dielectric constant materialson Si and conducting substrates. The leakage current densities arid other electrical properties of Ta205 films are better than those reported by other researchers. High energy photons in UV and VUV region provides electronically excited states but not dissociated complexes. The low thermal mass of the substrate provides limited reaction processing capability. In this paper, we will present the role of high energy photons in reducing the microscopic defects and the processing time. The photoenhanced surface diffusion allows the adsorbed atoms to adjust their bond geometries and occupy sites which result in overall reduction of stress and strain energy.

Formation of GaAsP Interface Layers Monitored by Reflectance Anisotropy Spectroscopy (RAS): P. Kurpas, A. Oster, M. Weyers, Ferdinand-Braun-Institut fur Hochstrequenztechnik berlin, Rudower Chaussee 5, D-12489 Berlin, Germany

Reflectance anisotropy spectroscopy (RAS) has been used to study the effect of different switching schemes in the MOVPE growth of GaInP/GaAs heterojunction bipolar transistors (HBT). The study focuses on the arsenic-by-phosphorus exchange at the interface of the GaAs base and the GaInP emitter. In a first step the formation of intermediate GaAsP layers was studied in dependence on PH3 purging time and H2 purging prior to PH3 exposure at different temperatures. Using GaAsP/GaAs superlattice structures the P-content was characterized ex-situ by transmission electron microscopy (TEM) and high-resolution X-ray diffraction (HRXRD). This yields a calibration of the RAS spectra against the composition. The obtained insights were then applied to the growth of HBT structures under RAS monitoring.