1:30PM, EE1+
"Interface Roughness Broadening of Intersubband Transitions:" K CAMPMAN, A. Imamoglu, A. Gossard, Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106
With the recent development of an intersubband laser1 and the proposal of a new class of optical devices based on quantum interference between intersubband transitions in semiconductor quantum wells, the understanding and control of the dynamics of intersubband transitions has become critical. In this work, we examine the mechanisms responsible for the broadening of intersubband transitions and their relative importance.
We have performed intersubband absorption measurements in single quantum wells of different well widths and alloy compositions. One series of samples consisted of four modulation doped Al0.3Ga0.7As/GaAs quantum wells grown consecutively differing only in the width of the quantum well (70, 80, 90, 105 Å). Absorption spectra measured at 4.2K show strong absorption peaks (20-30%) in the mid-IR with Lorentzian lineshapes. The linewidth (FWHM) was found to decrease monotonically from 4.4 meV to 2.5 meV as the well width is increased from 70Å to 105Å. This behavior is consistent with broadening dominated by interface roughness from the monolayer fluctuations typically present at MBE grown interfaces. For all samples measured the linewidth is found to remain constant as electrons are depleted from the well by the application of a gate bias. This is again consistent with interface roughness since electrons would be relatively ineffective in screening the well width fluctuations. The observed trend in linewidth is opposite to that expected for lifetime broadening due to optical phonons. For scattering by optical phonons, we would expect that wider wells would lead to decreased transition energy, shortened phonon lifetime, and broader absorption lines.
Another series of samples consisted again of four modulation doped quantum wells with Al0.3Ga0.7As barriers, but in these samples the well width was fixed at 100Å with differing alloy content in the well (Al0.05Ga0.95As, GaAs, In0.05Ga0.95As, In0.1Ga0.9As). The mobility in these structures is found to degrade strongly as Al or In is added to the quantum well due to alloy disorder scattering. The linewidth of the absorption peak, however, is found to remain relatively narrow for all alloy compositions. Thus, alloying will be an effective tool in the design of quantum well optical devices relying on intersubband transitions.
_____________________________________
1. Faist et al., Science 264, 553 (1994)
2. A. Imamoglu and R.J. Ram, Optics Lett. 19, 1744 (1994)
1:50PM, EE2
"GaAs(001) & (111)B Substrate Preparation Studied by Atomic Force Microscopy:" DAVID H. TOMICH, Nein Yi Li, Charles W. Tu, Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, CA 92122-0407
The conventional GaAs substrate preparation prior to growth in molecular beam epitaxy (MBE) includes a flash annealing (~600 - 650deg. C) under arsenic vapor pressure in the growth chamber. This flash annealing under arsenic vapor pressure can be a problem for mixed group V growths (e.g., As and P). Because of the high vapor pressure of arsenic required (typically ~10-5Torr) during the heating of the GaAs substrate, there can be a considerable amount of arsenic background pressure in the growth system. This arsenic background can lead to considerable intermixing at the interface when switching from GaAs growth to GaInP growth. The problem is sometimes referred to as the "memory effect" in MBE growth. A way of possibly minimizing this is affect is to desorb the oxide without an arsenic overpressure. Therefore, it is important to study the effects of oxide desorption with and without an arsenic overpressure.
Both GaAs(001) and GaAs(111)B surfaces were studied. Reflection high energy electron diffraction (RHEED) was utilized during the annealing process. RHEED gives an indication of an average surface roughness over the area of the electron beam "streak" and is commonly used to monitor the progress of surface deoxidization during the anneals. Scanning force microscopy (SFM) was utilized to map the surface roughness of the substrates before and after the anneal process.
GaAs(001) and (111)B substrates were prepared with a wet etch then indium mounted side by side on Si wafers which were subsequently mounted in a Perkin-Elmer MBE system for these studies. The substrates were slowly heated to ~600deg. C while periodically monitoring the RHEED patterns. Once the streaky RHEED patterns became visible the temperature was reduced to ~580deg. C and the substrates were annealed for 30 minutes, after which time the temperature was allowed to drop to room temperature and the substrates were removed from the growth chamber. The arsenic flux used to anneal the substrates was the same level as used during typical buffer layer growths. Arsenic limited RHEED oscillations indicate an incorporation rate of ~1.2 ML/sec.
SFM results indicate that there is little difference between the GaAs(111)B on-axis surfaces whether annealed with or without an arsenic overpressure. Both surfaces exhibit "egg carton" like features with sizes on the order of a couple of micrometers and apparent depths of up to 10 nanometers. The depth measurements may be probe limited. The GaAs(001) surfaces are much less prone to the "egg carton" like features found on the (111)B surfaces and show more variation between the surfaces oxide desorbed with and without an arsenic overpressure. Both GaAs(001) and (111)B surfaces are equally smooth after standard preparation and before annealing.
This work was partially supported by Wright Laboratories, Materials Directorate, USAF. 2:10PM, EE3
"Formation of Uniform GaAs Multi-atomic Steps with 20-30nm Periodicity and Related Structures on Vicinal (111)B Planes by MBE:" Y. NAKAMURA, Ichiro Tanaka, N. Takeuchi,S. Koshiba, H. Sakaki, RCAST,University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153, Japan; Quantum Transition Project, JRDC, 4-7-6 Komaba, Meguro-ku, Tokyo 153, Japan; Nikon Corporation, 471 Nagaodai-machi, Sakae-ku, Yokohama 244, Japan
We have investigated the MBE growth of GaAs layers on vicinal GaAs (111)B planes and studied, in particular, the periodicity and height of multi-atomic steps (MASs) by atomic force microscopy (AFM). We show that MAS with the typical period L of 20-30nm can be reproducibly formed by the choice of substrate orientation and growth condition. Specially, we discuss how the smoothness and the uniformity of MAS can be achieved.
Although most of GaAs-based devices are prepared on (001) substrates, (111) planes play important roles in various structures. For example, the selective growth of GaAs on patterned substrates results in facet structures, which consist of (001) and (111)B planes. These structures are used not only for some of practical laser diodes but also for the fabrication of ridge quantum wires (QWRs) and facet-edge QWRs1. In these QWRs, the surface smoothness of (111)B facet directly influences transport and optical properties of one-dimensional electrons as they accumulate at (111)B hetero-interfaces. Moreover, quasi-periodic MAS structures on the surface can be potentially used to form planar superlattice and coupled wire structures. Hence, we study in this work how the morphology of (111)B planes can be controlled.
We performed a systematic study on the MBE growth of GaAs on vicinal (111)B substrates and investigated how the morphology of MAS structures depends on the As flux and mis-orientation angle, [[Delta]][[theta]] of the substrate. The GaAs layers was grown with the growth rate of 0.27 um/hr and the substrate temperature of 580deg.C. In case of [[Delta]][[theta]] = 2deg., it is found that MAS structures can be formed uniformly when grown with the high As4 flux where As4/Ga ratio of beam equivalent pressure was ~ 130. Then, the typical period of MAS was 20-30 nm whereas the height of MAS is 0.5-1.0 nm. In contrast, when grown with the low As4 flux, corresponding to the As4/Ga ratio of ~50, MAS structures turned out to be inhomogenious. Similar results were obtained when grown on a substrate with smaller, [[Delta]][[theta]] of 1deg. even with the high As4 flux.
We studied also the morphology of (111)B planes in facet structures. Here, the (111)B facets are deliberately tilted by growing the structure on mesa-stripes, which is misoriented by, [[Delta]][[theta]] with respect to [110] orientation. As of the mesa-stripes increases from 2deg. to 7deg. , the amplitude [[Delta]] of MAS structures on the facets increases from 1 nm (~3ML) to 4nm (~12ML) with typical periods [[Lambda]] of 30 - 60 nm. These data indicate that [[Delta]][[theta]] of mesa-stripe should be minimized ([[Delta]][[theta]]<2deg.) to achieve smoothness of facet planes.
In summary, we studied the surface morphology of MBE-grown GaAs on vicinal (111)B planes and clarified ways to control surface smoothness and the uniformity of multi-atomic steps.
_____________________________________
1Y. Nakamura et al, Appl. Phys. Lett. 64, 2552 (1994).
2:30PM, EE4
"Kinetic and Thermodynamic Limitations to Molecular Beam Epitaxy of InAs/GaSb Heterostructures:" M.E. TWIGG, B.R. Bennett, P.M. Thibado, B.V. Shanabrook, L.J. Whitman, Naval Research Laboratory, Code 6812, 4555 Overlook Ave., Washington, D. C. 20375-5347
The novel properties of many semiconductor devices depend on the ability to grow thin layers with thickness and composition controlled on an atomic scale. This degree of control can be achieved by molecular beam epitaxy (MBE), because, under thermodynamic equilibrium, the deposited atoms (i.e. adatoms) may form a smooth and uniform surface. However, kinetic and thermodynamic limitations may dictate otherwise. When the diffusing adatoms do not have the opportunity to seek out their equilibrium positions, the resulting surface may not be smooth. Instead, the adatoms may find themselves bunched together in clusters, or may leave clusters of unfilled (vacancy) sites. These clusters give the surface a jagged morphology. When a layer of different composition is deposited onto such a surface, the resulting interface is rough as well. Therefore, in order to allow diffusing adatoms sufficient time to find their equilibrium positions, one might halt the growth between deposition steps, and thereby allow the adatoms more time to find their equilibrium positions.
We attempted to grow more abrupt interfaces for an 8 monolayer (ML) InAs quantum well grown on (100) GaSb at a temperature of 400deg.C, by using 100 second interrupts between deposition steps. Using in-situ scanning tunneling microscopy, we found that the introduction of such interrupts led to a locally smoother interfacial surface, as would be expected from a surface grown closer to equilibrium. But, surprisingly, cross-sectional high-resolution transmission electron microscopy (HRTEM) of the quantum well sample, showed that the introduction of interrupts led to intermixing on the order of 2 ML. This observation implies that the same kinetic effects that allow the formation of a desirable interfacial surface may also result in unwanted intermixing.
2:50PM, EE5
"InAs-on-GaSB and InAs-on-AlSB Interface Stability Measurements Using Line-of-Sight Mass Spectrometry": R. KASPI, Wright State University, University Research Center, Dayton, OH 45435; K.R. Evans, Wright Laboratory, Solid State Electronics Directorate, Wright-Patterson AFB, OH 45433
The novel properties of many semiconductor devices depend on the ability to grow thin layers with thickness and composition controlled on an atomic scale. This degree of control can be achieved by molecular beam epitaxy (MBE), because, under thermodynamic equilibrium, the deposited atoms (i.e. adatoms) may form a smooth and uniform surface. However, kinetic and thermodynamic limitations may dictate otherwise. When the diffusing adatoms do not have the opportunity to seek out their equilibrium positions, the resulting surface may not be smooth. Instead, the adatoms may find themselves bunched together in clusters, or may leave clusters of unfilled (vacancy) sites. These clusters give the surface a jagged morphology. When a layer of different composition is deposited onto such a surface, the resulting interface is rough as well. Therefore, in order to allow diffusing adatoms sufficient time to find their equilibrium positions, one might halt the growth between deposition steps, and thereby allow the adatoms more time to find their equilibrium positions.
We attempted to grow more abrupt interfaces for an 8 monolayer (ML) InAs quantum well grown on (100) GaSb at a temperature of 400deg.C, by using 100 second interrupts between deposition steps. Using in-situ scanning tunneling microscopy, we found that the introduction of such interrupts led to a locally smoother interfacial surface, as would be expected from a surface grown closer to equilibrium. But, surprisingly, cross-sectional high-resolution transmission electron microscopy (HRTEM) of the quantum well sample, showed that the introduction of interrupts led to intermixing on the order of 2 ML. This observation implies that the same kinetic effects that allow the formation of a desirable interfacial surface may also result in unwanted intermixing.
3:30PM, EE6+
"Epitaxial Dysprosium Phosphide Grown by Gas Source MBE on Gallium Arsenide:" R.J. HWU=, L.P. Sadwick, M. Patel, P. Lee, M. Nikols, P.C. Taylor, J. Viner, R. Alvis, R.T.Lareau, D.C. Streit, Department of Electrical Engineering, University of Utah, 3280 MEB, Salt Lake City, UT 84112; Department of Materials Science, University of Utah, Salt Lake City, UT 84112; Physics Department, University of Utah, Salt Lake City, UT 84112; AMD, One AMD Place, MS 32, Sunnyvale, CA 94088; Army Research Labs, Electronic & Power Source Dept., Fort Monmouth, NJ 07703; TRW, One Space Park, Redondo Beach, CA 90278
We report details of the magnetic, electrical, and optical properties of epitaxial dysprosium phosphide (DyP) grown on gallium arsenide (GaAs). DyP is highly lattice matched to GaAs, with the room temperature mismatch being less than 0.01%. We have grown DyP on GaAs by gas source molecular beam epitaxy using custom-designed group V thermal cracker cells and group III high temperature effusion cells. High quality DyP epilayers, as determined by X-ray and TEM measurements, were obtained for growth temperatures ranging from 450 to 600deg.C at DyP growth rates of approximately 1 um/hr.
The DyP epilayers are n-type with measured electron concentrations on the order of 3 to 4 x 1020 cm-3 with mobilities of 250 to 300 cm2/Vs. A consistent barrier height of 0.8 eV to GaAs is obtained from current versus voltage and capacitance versus voltage measurements.
Material and surface science properties of DyP/GaAs to be reported include Hall results, two-theta and double-crystal X-ray diffraction spectra, scanning electron and transmission electron microscopy results and secondary ion mass spectroscopy. DyP/GaAs is stable in air with no apparent oxidation taking place, even after months of ambient exposure to untreated air. Detailed results of optical absorption including FTIR, photothermal deflection spectroscopy, and transmission studies coupled with variable temperature magnetotransport measurements will be presented.
3:50PM, EE7
"Growth of InGaAsP on InP DFB Laser Gratings by Solid Source Molecular Beam Epitaxy:" W.-Y. HWANG, J.N. Baillargeon, A.Y. Cho, S.N.G. Chu, P.F. Jr. Sciortino, Bell Laboratories, Lucent Technologies, 600 Mountain Ave., Murray Hill, NJ 07974
Distributed feedback (DFB) lasers at 1.3 and 1.55 um wavelength employing InGaAsP/InP materials are crucial components for optical fiber communications. They provide such important features as single wavelength operation, narrow spectral width and high power efficiency. Fabrication of a high quality DFB laser structure require growth on a corrugated crystal surface with precise control of material composition and layer thickness. When the DFB grating is located below the lower confinement layer, the growth surface must be mechanically smooth after only a few hundred angstrom of the quaternary is deposited. Liquid phase epitaxy was first to demonstrate that planarization of DFB corrugated gratings was possible, but it is unable to precisely control the layer thickness. Presently, all commercially available DFB lasers are prepared exclusively by metalorganic chemical vapor deposition. Other growth techniques, such as chemical beam epitaxy and gas source molecular beam epitaxy (MBE), have met with much less success. Owing to the lack of a stable phosphorous source, solid source MBE growth of InGaAsP on etched grating surface has never been investigated.
MBE growth of quaternary InGaAsP layers on etched (100) InP grating surfaces
using all solid sources was studied. Elemental In and Ga, and P2 and AS2
supplied via solid phosphorous and arsenic valved sources were used. Gratings
with a periodicity of 0.2 um were optically patterned parallel to the [0
1]
direction using holographic photolithography, and then wet chemical etched to
form (111) A side-walls. The etched depth of the V-groves was about 600Å.
The mass transport properties for InP under a P2 beam flux in relation to the
grating profile and depth were first studied. Surface temperature was found
most critical for reshaping the grated surface. Grating depth was reduced by
50% after heating at 480deg.C and was nearly unobservable when heated at
510deg.C. InGaAsP layers were grown directly on the heat-treated InP grating
surfaces at temperatures ranging from 500deg.C to 530deg.C immediately
following heat treatment. As expected, higher growth temperature required
thinner InGaAsP growth to produce a smooth surface. Transmission electron
micrograph revealed that less than 500 Å of InGaAsP growth was required
to achieve a mechanically flat surface on heat-treated gratings with grove
depths between 300 Å and 500 Å.
4:10PM, EE8+
"Determination of Lattice Matched GaInP/GaAs and AlInP/GaAs Heterostructure Band Discontinuities Using Optical Techniques:" H.C. KUO, J.M. Kuo*, Y.C. Wang*, D.K. Sengupta, D. Tumbull, S. Bishop, G.E. Stillman, Department of Electrical and Computer Engineering, Microelectrics Laboratory and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801; *AT&T Bell Laboratory, 600 Mountain Ave., Murray Hill, NJ 07974
The (AlxGa1-x)0.5In0.5P/GaAs material system has a number of advantages over the AlxGa1-xAs/GaAs material system for HBT applications. In particular, the (AlxGa1-x)0.5In0.5P/GaAs heterojunction has a larger valence band offset and a smaller conduction band offset. However, the reported values for the valence band offset ratio (Qv) deduced from optical and electrical measurements vary over a wide range from 0.52 to 0.93 for GaInP/GaAs heterostructures1-6 and from 0.42 to 0.53 for AlInP/GaAs heterostructures2,7. The discrepancy between these values is quite impressive and it can be attributed to several reasons: 1) the growth technique associated with the various samples may produce different band offsets, especially if the ordering effect occurs in MOCVD grown samples at different growth temperature; 2) the reliability of the measurement techniques used and the experimental condition in that the accuracy of electrical or optical measurement, for offset determination are limited to the mV scale, yet a combination of inadequate theory, materials, growth and technological uncertainties limit their usefulness to the tens of mV scale; 3) intermixing of the interface may change the shape of quantum well resulting in the shift of transition energies and ultimately making the determination of band-offset rather ambiguous. The purpose of this talk is to report the measurement of band discontinuities of high quality GaInP/GaAs and AlInP/GaAs heterostruccums, enabling us to discriminate between the earlier, discordant results.
In these studies, two set of samples were grown by gas source molecular beam epitaxy (GSMBE) at 530deg.C. MQW samples consisting of thirty periods of nominal 300 Å, GaInP(AlInP) barrier and 100 Å GaAs quantum well were grown for Photoluminescence Excitation (PLE) measurements, while GaInP/GaAs (AlInP/GaAs) 5 SQW with different well width (30, 50, 70, 100, 150 Å ) were grown for Photoluminescence (PL) measurements, respectively. The optimum residual group-V source evacuation time (RSE) was used to eliminate the intermixing layers between GaInP/GaAs (AlInP/GaAs) heterostructures. HR-TEM lattice image shows high quality interfaces with fluctuations of 1 or 2 monolayers. Thus, the simple square quantum well model can be utilized to calculate the confined energies. The composition of barrier was determined by double crystal x-ray diffraction (DCXRD) and the well thickness was measured by XTEM. Based on the thickness and composition determined by XTEM and x-ray simulation, the transition energies of MQWs were calculated using three-band Kane model with different band-offset ratio. The best fit of PLE data and calculated energies suggest that the Qv was 0.63+/-0.02 for GaInP/GaAs and 0.54+/-02 for AlInP/GaAs heterostructures, and the values were independent of temperature. With the band-offset ratio determined by PLE measurements, we calculated the first (HHl -Cl) transition energy for SQW with different well thickness. By taking into account of Stokes Shift (~4.4 meV), the PL energies for the five SQW give good agreement with the calculated results.
In conclusion, we have measured the valence- and conduction-bandedge discontinuities for GSMBE grown GaInP/GaAs and AlInP/GaAs heterostructures using PL and PLE technique. The results are in reasonable agreement with the electrical measurements1,2,5 and Tiwari's empirical model calculation8 .
_______________________________________
1. M.A. Rao, E.J. Caine, H. Kroemer, S.I. Long, and D.I. Babic, Appl. Phys.
Lett. 61, 641 (1987).
2. M.0. Watanabe and Y. Okiba, Appi, Phys. Lett. 50, 906 (1987).
3. M.A. Haase, M.J. Hafich. and G.Y. Robinson, Appl. Phys. Lett. 58, 616
(1991).
4. J. Chen, J. R. Sites, J. L. Spain, M. J. Harich. and G.Y. Robinson, Appl.
Phys. Lett. 58, 744 (1991)
5. C. Biswas, N. Debbar, P. Bahattacharya, M. Razeghi, M. Defour and F. Omnes,
Appl. Phys. Lett. 56, 833 (1990).
6. T. Kobayashi et al., J. Appl. Phys. 65, 4898 (1989).
7. S. L. Feng et al., Semiconductor Sci. Technol. 8, 2092 (1993).
8. K. Interholzinger et al., EMC E9 A10 (1995).
9. S. Tiwari and D.J. Frank, Appl. Phys. Lett 60, 630 (1992).
4:30PM, EE9
Hydride-Free Chemical Beam Epitaxy Processes and Application to GaInP/GaAs Heterojunction Bipolar Transistors: J. CH. GARCIA, C. Dua, Thomson-CSF, Central Research Laboratories, Domaine De Corbeville, 91401 Orsay Cedex, France; M. Saeed, D. Pavlidis, The University of Michigan, Department of Electrical Engineering and Computer Science, Ann Arbor, MI 48109-2122
Large development efforts have been devoted to the replacement of highly toxic arsine and phosphine gaseous sources by organo-metallic compounds in both MOCVD and CBE technologies. The potential candidates in CBE are tDMAAs, TBAs and TBP for arsine and phosphine respectively. These sources have been used in order to study the feasibility of Heterojunction Bipolar Transistor (HBTs) and their characteristics have been reported in the past by the authors. In this paper, we present an extension of the above approach towards the establishment of a reproducible manufacturing process as necessary for HBT realization using a complete hydride free gaseous growth process.
A multi-wafer 3[[yen]]2" hydride and hydrogen-free CBE machine V90 of VG has been qualified for this purpose and an epitaxial process has been developed which allowed excellent characteristics in terms of composition, thickness uniformity and reproducibility of growth parameters (temperature, growth rate, doping). As an example, growth rates only exhibit a drift of 3% over a period of one year of operation. 3x2" composition uniformity for both GaInP and GaAlAs are better than 500ppm. Total defect densities of less than 10 def/cm2 are obtained routinely.
While tDMAAs is dissociated on the growing surface, TBP and TBAs have to be precracked. The cracking of TBAs is found complete even at cracker temperatures as low as 700deg.C. For TBP, the cracking was found dependent on the design of the cracker cell, the main parameter being the cell operating pressure (high, medium or low pressure). Under optimal conditions, the cracking of TBP into P2 is found complete. However, the complete cracking of the molecule induces strong carbon incorporation in the (Ga)InP layers. The lowering of the cracker temperature of about 50deg.C is able to reduce significantly the carbon incorporation at acceptable levels for device structures. No problems of stability or reproducibility of these group V sources have been encountered. In addition to GaInP, we have also investigated manufacturing processes using Gal-xAlxAs (x: 0-50%) where the presence of Al imposes even stricter process control. These have been studied using tDMAAs or TBAs and trimethylamine alane starting sources. Low levels of carbon and oxygen were detected by SIMS analysis independent of the aluminum concentration used ([O] = 8-5x1017cm-3, [C] = 2-5x1017cm- 3.
Carbon doped Heterojunction Bipolar Transistors in both GaInP/GaAs and GaAlAs/GaAs material systems have been fabricated to verify the established material manufacturing processes. High current gain ranging from 60 to 200 for base sheet resistances of 430 to 170 ohm square have been obtained. A comparison of various HBT types and a study of the influence of the starting sources on the electrical performance of the devices will be presented.
Work supported by THOMSON-CSF and ARO/URI (Contract No.DAAL03-92-G-0109).
4:50PM, EE10+
"Exploration of the Properties of GaAs and InP Compliant Substrates for Extension of the Critical Thickness and Strain-Modulated Epitaxy:" CARRIE CARTER-COMAN, Francoise Fournier, April S. Brown, Robert Bicknell-Tassius*, Nan Marie Jokerst, School of Electrical and Computer Engineering, Georgia Institute of Technology, 791 Atlantic Drive NW, Atlanta, GA 30332-0269; *Georgia Tech Research
The use of compliant substrates is increasingly recognized as a new concept to extend the limits of the conventional critical thickness for strained overlayer growth. By utilizing a thin substrate, part of the strain can be accommodated in the substrate, allowing the growth of high quality epilayers in regimes where defect formation ordinarily degrades the material. Recently we reported on a new type of compliant substrate technology using thin film substrate material.1 It has been demonstrated that high quality thin film GaAs compliant substrates can be fabricated and that these films are not degraded during the usual heating and cooling cycles necessary for growth and characterization. Furthermore, it has been shown that strained InGaAs epilayers grown on conventional GaAs substrates relaxed before epilayers grown simultaneously on thin film compliant substrates. An additional unique aspect of this compliant substrate technology is that the substrates can be patterned on the bottom, bonded surface, thus creating an unpattemed growth surface in which the strain can be laterally modulated. This strain modulation can be paired with strain-dependent MBE growth kinetics to produce epilayers which vary in composition and thickness across the sample. The first demonstration of this concept, strain-modulated epitaxy, has been presented.2 It has been shown that thin film GaAs bottom patterned compliant substrates can be grown on and that the pattern affects the growing epilayer.
Recent results concerning GaAs and InP compliant substrates will be presented. The fabrication and characterization of the first thin film InP compliant substrates and the growth of strained In0.66Ga0.34As on InP compliant and conventional substrates will be presented. For 400 NM-thick epilayers, the total strain in the InGaAs on the compliant substrates was less than that in the InGaAs grown on the InP substrates as seen by (400) and (511) double crystal x-ray diffraction measurements. Double crystal x-ray diffraction performed on the (400) indicates that the peak separation is less on compliant substrates and that the InGaAs has a smaller FWHM compared to the conventional substrates. The (511) measurements indicate that the InGaAs lattice constant on the compliant substrates is more than 10 times closer to the bulk value than the InGaAs grown on conventional substrates. These results indicate that there is accommodation of strain in the InP compliant substrates. These results will be contrasted to the latest results on the GaAs compliant substrates.
Characterization of the compliant substrate growths by double crystal x-ray diffraction and low temperature photoluminescence will be discussed and new ideas for thoroughly exploring the properties of the compliant substrates will be introduced. The ongoing process development for developing bigger, more versatile, compliant substrates and bottom-patterned compliant substrates for the next generation of experiments will be summarized.
____________________________________
1. C.A. Carter, A.S. Brown, N.M. Jokerst, D.E. Dawson, Z.C. Feng, K.C.
Rajkumar, and G. Dagnall, presented at the Electronic Materials Conference,
1995.
2. C.A. Carter, A.S. Brown, R. Bicknell-Tassius, N.M. Jokerst, F. Fournier, and
D.E. Dawson, presented at the North American Conference on Molecular Beam
Epitaxy, 1995.
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