Selective Area Omvpe Growth of Gainp on Patterned GaAs Substrates using Semimetallic Amorphous Carbon Mask
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KEITH L. WHITTINGHAM*, BOBBY L. PITrS*, GREGORY F. REDINBO** AND JAMES R. SHEALY* *OMVPE Facility, School of Electrical Engineering, Cornell University, Ithaca, NY 14853 **School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853
ABSTRACT
In this study, we have investigated the effectiveness of semimetallic, amorphous carbon films as a liftoff mask in the selective growth, by OMVPE, of GaInP epitaxial layers, on (001) oriented GaAs substrates. Scanning electron microscopy, cathodoluminescence spectroscopy and EDX analysis have been employed to characterize the epitaxial material. Our results show excellent selectivity with little nucleation taking place on the amorphous carbon mask in the region of the patterned openings. Liftoff of the carbon mask was very easily achieved, leaving no unintentional nucleation on the substrate below. Investigations in the AlGaAs/GaAs system did not yield the same degree of selectivity with this mask, but the polycrystalline film that deposited on the maskwas cleanly lifted from the substrate by the liftoff of the mask. INTRODUCTION
Selective epitaxy of III-V semiconductor materials has been ardently investigated over the past several years, particularly in the pursuit of optoelectronic integration. Among the features of selective epitaxy that have been studied and exploited are the variation of growth rate with feature size, the variation of feature profile with crystallographic orientation, and the dependence of local group III mole fraction on feature size'-,. Recent accomplishments making use of these properties include single-growth-step fabrication of buried-quantum-well laser diodes7, the fabrication of several quantum-wire-like structures', 3' 8 and the observance of large band-gap shifts in multi-quantum-well structures 9. The majority of selective epitaxy studies reported to date involved the AlGaAs/GaAs, InGaAs/InP and InGaAsP/InP material systems. Relatively few studies have focused on the GaInP/GaAs material system3"8. Studies have also traditionally focused on the use of the dielectric materials, SiO2 and Si N, as selective epitaxy masks, due to their established use in semiconductor device processing. Recently, significant attention has been paid to the use of semimetallic, amorphous carbon (a-C) films in various stages of device processing. This interest is justified due to the known low reactivity and low diffusion coefficient of carbon. Experiments have been performed using a-C as an etch mask for chemically assisted ion beam etching (CAIBE)'° and as a diffusion barrier in Cu metallization". In this study we investigate, for what we believe to be the first time, the use of a-C as a liftoff mask material in the selective epitaxy of III-V semiconductor materials by OMVPE.
55 Mat. Res. Soc. Symp. Proc. Vol. 326. ©1994 Materials Research Society
EXPERIMENTAL PROCEDURE
GaAs wafers of (001) orientation were degreased in solvents and etched in a mixture of H 2so 4:HI20 2:H20 (5:1:1) for 15 minutes. These were then soaked in HF, rinsed, and then
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