About the 8th Biennial Workshop on OMVPE: Technical Program, Thursday Morning Sessions (April 17)

The following papers will be presented at the 8th Biennial Workshop on OMVPE, on Thursday morning, April 17th, 1997. The calendar of events describes the entire technical program.

SESSION X: NITRIDES III

Characterization of GaN Stripes Grown by Selective-Area Metalorganic Chemical Vapor Deposition: Xiuling Li, S. David Roh, and James J. Coleman, Microelectronic Laboratory, University of Illinois, Urbana, IL 61801

We report the selective-area metalorganic chemical vapor deposition of GaN stripes in the size range of 50 to 125 mm and the characterization of the morphology, topography and optical properties of these stripes. GaN films (~ 1- 3 mm) grown on (0001) sapphire are used as the substrates for patterning. Excellent selectivity is observed and smooth surface morphology has been achieved under optimized growth conditions which require a higher V/III ratio than broad area growth. It is found that (0001) terraces of ~5 mm in width appear at the edges of all stripes in thick- samples, independent of stripe size and orientation variation. The selectively grown GaN yields stronger band-edge emission than the "substrate" GaN, indicating material quality improvement. However, donor-acceptor pair recombination or conduction band to acceptor transition and yellow emission are also enhanced in certain areas of the stripe. The spatial correlation of these emission bands is established by cathodoluminescence wavelength imaging, and the origin of these emissions is speculated.

8:40 am

OMVPE Growth and Characterization of High Quality InGaN Films: Wim Van Der Stricht, Ingrid Moerman, Piet Demeester, University of Gent, Department of Information Technology-IMEC, Sint-Pietersnieuwstraat 41, 9000 Gent, Belgium, Ted Thrush and John Crawley, Thomas Swan & Co. Ltd., Button End, Harston, Cambridge, CB2 5NX, UK

Recently the group IIInitrides (In, Ga)N have attracted much attention because of the high potential for the fabrication of light emitting devices operating in the red to ultraviolet wavelength range. Despite the recent success in realizing devices, only few reports have been made on growth of InGaN. In this paper growth of high quality InGaN films on (0001) sapphire substrates by atmospheric pressure organometallic vapor phase epitaxy in a vertical rotating disk reactor is investigated. Several growth parameters are varied to optimize the InGaN layer quality: carrier gas and flow rate, growth temperature, VIII ratio and rotation speed. The layers are characterized by DC xray and photoluminescence measurements. The InGaN layers are transparent and show no In-droplets on the surface. The In-content varies between 25 and 6 % for growth temperatures between 800 and 850°C. The DC x-ray rocking curve of InGaN typically shows a FWHM from 12 to 9 arcmin. Room temperature PL shows an intense band edge emission with a FWHM between 200 and 100 meV for an Incontent of 13 and 2%.

9:00 am

Growth of GaN Films on Compliant Silicon-on-Insulator (SOI) Substrates: Jun Cao, Dimitris Pavlidis, Yongjo Park, Jasprit Singh, and Andreas Eisenbach, Solid State Electronics Laboratory, Dept. of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, MI 48109-2122

GaN and related nitrides find several applications in UV/blue light emitters and high temperature electronics devices. Although extensive efforts have been made to achieve high quality GaN material, the quality of epitaxially grown GaN films is still hindered by the large lattice mismatch between GaN and commonly used substrates such as sapphire, silicon and GaAs. This leads to high interfacial strain between the epilayer and the substrate and as a result, interfacial dislocations are generated. The latter propagate along the epilayer growth direction and produce threading dislocations which are running through the layer and limit therefore its use for device applications. The new, drastically different epitaxial growth approach described here allows growth of the GaN layer on a "soft" buffer which complies to the lattice constant structural requirements of the epitaxial film and results in fewer defects. The thin silicon on oxide layer of the employed Silicon-on-Insulator (SOI) wafer acts as compliant buffer and satisfies not only the requirements for higher quality compliant growth but is also compatible with large wafer size epitaxial techniques. GaN layers have been grown on SOI substrates by low pressure rnetallorganic chemical vapor deposition (LPMOCVD) under various growth conditions and compared with GaN films grown on Si substrates. The crystal uniformity, surface morphology and threading dislocations of GaN films grown on SOI substrates show improved properties compared with layers grown directly on Si substrates as evidenced by Xray diffraction spectroscopy (XRD) and transmission electron microscopy (TEM). Full width at half maximum (FWHM) XRD values improved from 672arcsec to 378arcsec by growth on SOI. The background carrier concentration and carrier mobility are also superior for GaN on SOI as compared with GaN grown on Si. Minimum carrier concentration and maximum mobility for GaN on SOI at RT are 3.8xl017cm-3 and 320cm2/(Vs), respectively. Work supported by ONR contract no. N00014-92-J-1552.

9:20 am

Growth and Characterization of InGaN Quantum-Well Heterostructures: P.A. Grudowski, C.J. Eiting, J. Park, B.S. Shelton, D.J.H. Lambert, and R.D. Dupuis, Microelectronics Research Center, The University of Texas at Austin, Austin TX 78712-1100

Data are presented on the growth of InxGal-xN/InyGal-yN heterostructures by low-pressure metalorganic chemical vapor deposition on sapphire substrates. These InGaN single layers. Double-heterostructures (DH), and quantum-wells (QW's) have been grown using trimethylgallium, trimethylindium, and ammonia using both H2 and N2 carrier gases. The InGaN growth rate and alloy composition are found to depend upon the growth temperature and the In incorporation is strongly dependent upon growth kinetics. The films have been characterized by photoluminescence (PL), cathodoluminescence (CL), x-ray diffraction, and transmission electron microscopy. PL spectra of single InGaN films and double heterostructures show relatively narrow widths with the narrowest PL measured for the films grown at the higher temperatures. The 300K PL spectra from l0-period MQW structures (5 nm In0.20Ga0.80N wells, 10 nm In0.05Ga0.95N barriers) grown at 730° reveals intense 435 nm emission with a FWHM of ~45nm. Narrow 4.2K PL spectra for the bulk InGaN layers (FWHM~5.8 nm for ~11) and the MQW heterostructures and 300K CL data revealing spatially uniform luminescence will also be presented.

9:40 am

Growth and Structural Characterization of Al xGa 1-xN Layers and Al xGa 1-xN/GaN Heterostructures Deposited by OMVPE: A.Y. Polyakov, M. Shin, J.A. Payne, M. Skowronski, D.W. Greve*, and A.V. Govorkov**, Dept. Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, *Dept. Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, **Institute of Rare Metals, B. Tolmachevsky, 5, Moscow, 109107, Russia

It is well known that with increasing Al mole fraction, the electrical and optical properties of AlGaN layers deteriorate. These effects are commonly ascribed to degradation of crystalline quality of AlGaN with increase in Al composition. In this work a series of AlxGa1-xN layers with composition ranging from x=0 to x=1 was grown by OMVPE on sapphire substrates using thin GaN nucleation layers. Characterization included high resolution x-ray diffraction (HRXRD), atomic force microscopy (AFM), and microcathodoluminescence (MCL). It is shown that the half width of both symmetric and asymmetric x-ray diffraction peaks increases rapidly with the increase in Al mole fraction and is a strong function of the layer thickness. This allowed to determine the thickness of semi-sound growth zones in AlGaN films as a function of composition. The growth of AlGaN on thick (>1mm) GaN layers of high crystalline quality, produced ternaries of higher structural perfection. However, deposition of AlGaN cap layer results in considerable amount of strain in underlying GaN layer. This is believed to result in the lower electron mobility in 2 DEG structures. AFM studies show that all AlGaN layers grew by atomic step flow mode. We will report on initial stages of AlGaN growth on GaN/Al2O3 composite substrates as a function of aluminum content and GaN thickness, including nucleation of dislocations and strain relaxation mechanism in these structures. We will also report on observation and the origin of new type of defect in AlGaN films. These defects appear as hexagonal shallow (10 nm) depressions in the films that are never observed in undoped GaN layers. These defects affect the nonradiative recombination rate and produce a strong contrast in MCL images of the layers.

10:00 am Break