Low Pressure Growth of GaAs/AlGaAs Layers on 2N and 3N Substrates in a Multiwafer Reactor
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LOW PRESSURE GROWTH OF GAAS/ALGAAS LAYERS ON 2N AND 3N SUBSTRATES IN A MULTIWAFER REACTOR
M. Heyen, M. Heuken*, G. Strauch, D. Schmitz, H. Jurgensen and K. Heime* AIXTRON GmbH, Julicher Str. 336-338, D-5100 Aachen, FRG *Inst. of Semicond. Electr., University Duisburg, Kommandantenstr. 60, D-4100 Duisburg 1, FRG ABSTRACT The epitaxial growth of GaAs/AIGaAs layers and multilayer structures has been investigated in different low pressure horizontal multiwafer reactors for high throughput capable to handle several 2" and 3" wafers in one run. The growth behavior in these reactors will be described with respect3 to gas flow dynamics. The background carrier concentration is in the 1014 cm- range. The uptake of dopants (SiH 4) is strongly reduced upon pressure reduction. The uniformity of GaAs and AIGaAs layer thickness is better than + 3 % over 3' diameter substrates. The uniformity of composition (measurer on HEMT structures) is better than + 1 % across 98 % of the wafer areas (+ 0.5 % across 75 %). Also the reproducibility is better than 1 %. Results on tiFe uniformity of dopant distribution will also be presented. HEMT structures grown at low pressure conditions show mobilities of 100,000 cm 2/Vs at 77 K and over 210,000 cm 2/Vs at 20 K (n,= 6x10"1 cm- 2, spacer thickness 9 nm). HEMT devices with transconductance of 330 mS/mm could be achieved. INTRODUCTION Industrial exploitation of multi quantum well and HEMT structures have emphasized the development of epitaxial reactor systems with thu capability of growth on several wafers at a time. Especially GaAs device linns standardize on 3" wafer diameters. With respect to the strong efforts made in the InP-sector a reactor for industrial application should also meet the requirements of this material system. Low pressure MOVPE is a technique which basically solves the problems of precise growth controllability of all material systems. Considerations of growth kinetics and gasflow dynamics lead to a model that turns out a linear horizontal reactor system operating at reduced pressures to be an adequate solution for homogeneous growth of abrupt transitions in layer structures on large substrate areas. Furtheron for HEMT -structures a precise controlled growth of considerably thin but highly doped layers followed by extremely low doped material is required. Low pressure growth reduces uptake of more volatile dopants and thus decreases background carrier concentration. The controllability of intentional doping is improved, since the amount of dopant to be used for a certain doping level is increased in comparison to atmospheric pressure operation. Based on these considerations LP - MOVPE processes have been developed applic able for small scale and large scale production reactors capable to grow on several 3' wafers. Mat. Res. Soc. Symp. Proc. Vol. 145. 01989 Materials Research Society
246 EXPERIMENTAL The basic processes have been developed in the standard size AIXTRON LP MOVPE reactor. This type for two 2" wafers has been described in various publications /1, 2/. A straig
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