Contains reports on three research projects and a list of publications.3M Company Faculty Development GrantAT&T Research Foundation Special Purpose GrantDefense Advanced Research Projects Agency Subcontract 216-25013Defense Advanced Research Projects Agency Subcontract 542383Joint Services Electronics Program Contract DAAL03-89-C-0001National Science Foundation Grant ECS 88-46919National Science Foundation Grant ECS 89-05909U.S. Navy - Office of Naval Research Contract N00014-88-K-0564Charles Stark Draper Laboratories Contract DL-H-418484Defense Advanced Research Projects Agency Subcontract 530-0716-0

Coronado, Christopher A.

Ho, Easen

Huber, Carmen

Kolodziejski, Leslie A.

Nanto, Hidehito

Odoardi, Angela R.

Shepard, Stephen C.

DSpace@MIT

Chapter 6. Chemical Beam Epitaxy of Compound SemiconductorsChapter 6. Chemical Beam Epitaxy of CompoundSemiconductorsAcademic and Research StaffProfessor Leslie A. Kolodziejski, Stephen C. ShepardVisiting Scientists and Research AffiliatesDr. Hidehito Nanto,1 Dr. Carmen Huber 2Graduate StudentsChristopher A. Coronado, Easen HoTechnical and Support StaffAngela R. Odoardi6.1 Chemical Beam EpitaxyFacilitySponsors3M Company Faculty Development GrantAT&T Research FoundationSpecial Purpose GrantDefense Advanced Research Projects AgencySubcontract 216-25013 and 542383Joint Services Electronics ProgramContract DAAL03-89-C-0001National Science FoundationGrants ECS 88-46919 and ECS 89-05909U.S. Navy - Office of Naval ResearchContract N00014-88- K-0564Our new laboratory for the chemical beam epitaxy(CBE) of both II-VI and III-V compound semicon-ductors finally began to take the form of a workingresearch facility in 1990. The substantial labora-tory renovation was completed in February; theCBE system hardware was delivered in March andinstalled throughout most of the summer; ZnSewas deposited onto GaAs substrates in earlyAugust. However, the modular CBE system is notcomplete yet. We are anticipating delivery of theanalytical/metalization chamber and aIll-V-dedicated gas source molecular beam epitaxy(GSMBE) system. Both chambers will beattached to the periphery of the ultrahigh vacuum(UHV) transfer chamber. Figure 1 shows thesystem footprint complete with all chambers whichare currently expected. In the future, we plan toadd an in situ patterning chamber for further pro-cessing of the samples prior to removal from theUHV environment. The analytical metalizationchamber will contain Auger Electron Spectroscopy,reflection high energy electron diffraction, electronbeam evaporators for metals, and ports for photonillumination of the sample. The GSMBE systemwill be dedicated to the growth of arsenides,phosphides, and antimonides; solid elementalsources of In, Ga, Sb and Al will be utilized withgaseous hydrides of As and P. The chamber willbe employed for the fabrication of sophisticatedquantum-effect electronic devices, a variety ofoptoelectronic devices, and advanced II-VI/III-Vmultilayered heterostructures.6.2 Metalorganic MolecularBeam Epitaxy (MOMBE) ofZnSeSponsorsCharles Stark Draper LaboratoriesContract DL-H-418484Defense Advanced Research Projects AgencySubcontract 542383Joint Services Electronics ProgramContract DAAL-03-89-C-0001National Science FoundationGrant ECS 88-46919U.S. Navy - Office of Naval ResearchContract N00014-88-K-05641 Department of Electronics, Kanazawa Institute of Technology, Kanazawa, Japan.2 Physics Department, University of Puerto Rico, Rio Piedras, Puerto Rico.Chapter 6. Chemical Beam Epitaxy of Compound SemiconductorsFigure 1. Layout of the CBE laboratory showing the footprint of the modular UHV system. The five chambers arethe introduction, transfer, analytical/metalization, Il-VI CBE reactor, and Ill-V GSMBE reactor. Also indicated in thedrawing is the wet chemical station for substrate preparation.The II-VI semiconductor ZnSe is currentlyreceiving considerable attention due to the recentlyreported success of p-type doping. Once ZnSe issuccessfully doped, both n- and p-type, variousoptical devices such as laser diodes, opticalmodulators, etc., can take advantage of the2.67 eV bandgap to provide operation in theblue/blue-green portion of the spectrum. Themost successful n-type dopant has been Cl with1019 electron carrier concentrations reported formolecular beam epitaxy (MBE) growth. Thus far,incorporation of Li has been demonstrated toresult in p-type ZnSe. Electrical measurements toconfirm the presence of holes are complicated dueto the small hole concentrations and the problemassociated with forming ohmic contacts to p-typematerial. However, pn junctions formed in ZnSehave emitted blue light at room temperature. Dueto significant problems of Li interdiffusion, investi-gations are currently focusing on incorporatingdopant species other than Li to provide shallowacceptors. A potential candidate is nitrogen,although this volatile atom is difficult to incorpo-rate due to its small sticking coefficient and stabledimer bonding.Our objective is to study controlled substitutionaldoping of ZnSe, both n- and p-type, by employingthe growth technique of chemical beam epitaxy.CBE offers many advantages compared to MBE ormetalorganic chemical vapor deposition andemphasizes the use of gaseous sources in anultrahigh vacuum environment. In the CBE growthtechnique, the gaseous sources which are utilizedare both hydrides and metalorganics. It is anti-cipated that precise flux control of each specie viamass flow control of the gas will be a significantadvantage in the growth of the high vapor pres-sure II-VI compounds.We have grown ZnSe thin films on GaAs bulk sub-strates by metalorganic molecular beam epitaxy(MOMBE). MOMBE differs from CBE due to theabsence of the gaseous hydride sources. Themetalorganic gaseous sources which have beenemployed at present are diethylzinc (DEZn) anddiethylselenide (DESe). In the growth exper-iments, the metalorganics are "cracked" orthermally decomposed prior to impingement ontothe GaAs. The Zn and Se atoms are removed fromthe hydrogen and carbon atoms to allow the useof a lower growth temperature and to more closelyapproximate the MBE growth approach.Figure 2 shows the reflection high energy electrondiffraction pattern obtained from a 500A ZnSe filmgrown on GaAs. The presence of Kikuchi linesand a strongly streaked pattern suggest that theZnSe is of high quality and single crystalline. Thetwo-fold reconstruction lines observed in the[010] indicate a Zn-stabilized surface. For thegrowth of the thin ZnSe shown here, the substratetemperature was approximately 3000 C with 1.0and 0.30 sccm flow rates of DEZn and DESe,respectively. Investigations of the surface mor-phology with Nomarski interference microscopyhas indicated the presence of a featureless surfaceat 1000x magnification. Additional experimentsare in progress to increase the growth rate, as well44 RLE Progress Report Number 133Chapter 6. Chemical Beam Epitaxy of Compound SemiconductorsFigure 2. Reflection high energy electron diffraction patterns obtained from a 500A ZnSe film grown on a (001)GaAs substrate. (a) [110] azimuth and (b) [010] azimuth.as to investigate the growth using sources ofdimethylzinc and hydrogen selenide.6.3 Photon-assisted MOMBE ofWide Bandgap II-VI CompoundSemiconductorsSponsorsDefense Advanced Research Projects AgencySubcontract 530-0716-07National Science FoundationGrant ECS 88-46919To achieve our objective of fabricating p-typeZnSe, we are employing state-of-the-art epitaxialgrowth techniques, such as CBE and MOMBE, totake advantage of the nonequilibrium nature of thegrowth. At the same time, we are employing avariety of coherent photon sources to illuminate aportion of the GaAs substrate during growth.Photon-assisted MBE of ZnSe has been demon-strated to have an effect on (1) the incorporationof various atoms, (2) the stoichiometry of thegrowing surface front, and (3) the density ofdefects. In our laboratory, the CBE reactor hasviewports positioned so that a photon source canilluminate the substrate either perpendicular to orparallel to the surface. In our preliminary exper-iments, we have employed the visible 4579A lineof an argon ion laser perpendicular to the GaAssurface during MOMBE growth of ZnSe. The laserbeam was defocused to partially illuminate a 1 cmdiameter area of the wafer, providing a powerdensity of approximately 100 mW/cm 2. The powerdensity is sufficiently low so that there was verylittle temperature increase. Following growth, novisible differences in the surface morphology weredetected. However, a significant enhancement inthe growth rate was observed from thicknessmeasurements made by selectively etching awaythe ZnSe layer from the GaAs substrate. In thearea illuminated by the laser, the growth rate wasthree times greater than in the area which wasunilluminated. At the growth temperature of- 325°C, the wavelength of the laser is at anenergy above that of the ZnSe bandgap. We arecurrently preparing experiments to study in detailthe physical phenomena, for example electronic orphotochemical, responsible for the growth rateenhancement.The above mentioned results on the MOMBE ofZnSe, with and without photon assistance, arepreliminary and not at all conclusive. These datarepresent the very first results on films grown bythe MOMBE technique in our new CBE reactor.Additional microstructural, electrical, and opticalcharacterizations of the ZnSe films are currentlybeing prepared to provide further insight into theproperties of this very important wide bandgapsemiconductor.a bChapter 6. Chemical Beam Epitaxy of Compound Semiconductors6.4 PublicationsKolodziejski, L. A. "Modern Growth Technologiesof Semimagnetic Semiconductors." Paper pre-sented at the International School on Physicsof Semiconducting Compounds, Jaszoweic,Poland, April 1990.Kolodziejski, L. A. "Chemical Beam Epitaxy forAdvanced Optoelectronic Devices." Paper pre-sented at the Optical Society of AmericaMeeting, Boston, Massachusetts, November1990.46 RLE Progress Report Number 133

Chemical Beam Epitaxy of Compound Semiconductors

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Chemical Beam Epitaxy of Compound Semiconductors

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