CONDUCTION BAND DISCONTINUITY MEASUREMENTS AND CRYSTAL GROWTH CHARACTERIZATION OF THE ABRUPT GERMANIUM-GALLIUM - ARSENIDE HETEROJUNCTION

Germanium-gallium arsenide semiconducting heterojunctions have been fabricated by molecular beam epitaxy. The growth of germanium on gallium arsenide is discussed and compared with other techniques. The germanium films were grown both in arsenic-rich and relatively arsenic-free environments. The n-type doping is proportional to the arsenic(,4) background partial pressure during growth. The residual p-type impurity is attributed to crystal vacancies and not gallium as previously reported. The growth of gallium arsenide on gallium arsenide substrates of various crystal orientations is reported. The amphoteric behavior of the silicon dopant is seen to vary with the crystal orientation of the substrate. Silicon has previously been noted to be weakly amphoteric on the (100) orientation. Here it is seen to be strongly amphoteric on the (110) orientation. The behavior is seen to be in accord with theoretical predictions. Electrical and optical measurements are used to verify the silicon dopant behavior.; The theory of conduction band discontinuities is briefly reviewed, focussing on theories dealing with the (100) germanium-gallium arsenide heterojunction. Current-voltage measurements are used to measure the conduction band discontinuity of the n-n (100) germanium-gallium arsenide heterojunction. The doping of the germanium is varied between 1 x 10('18) cm('-3) and 4 x 10('19) cm('-3). The doping of the gallium arsenide is varied between 8 x 10('14) cm('-3) and 2 xn 10('17) cm('-3). The current-voltage characteristics are seen to vary systematically and reproducibly with doping, temperature, and post-growth heat treatments. The electrical barrier at the heterojunction is measured to be 80 (+OR-) 20 meV. From this measurement the conduction band discontinuity is estimated to also be on this order, which is in fine agreement with the theoretical results reviewed. The discrepancy with previous experimental results is discussed.