Materials and electrical characteristics of carbon-doped Ga 0.47In 0.53As using carbontetrabromide by MOMBE for HBT device applications

Abstract

Metalorganic molecular beam epitaxy (MOMBE) growth of C-doped Ga 0.47In 0.53As heterostructures and Ga 0.47 In 0.53 As InP heterostructure bipolar transistors (HBT) using carbontetrabromide (CBr 4) as the dopant source is reported. Hall, secondary ion mass spectrometry (SIMS), and X-ray data were used to characterize the bulk CGa 0.47In 0.53As material. The incorporation of C showed a power dependence on the group V beam flux of −0.29 and −0.75 for solid arsenic and AsH 3 sources, respectively. This may be related to the change in group V vacancy concentration as the group V beam flux is varied. X-ray measurements of C-doped layers indicated a contraction in the lattice parameter larger than would be calculated using Vegard's law. Doping levels from 2 × 10 17 to 7 × 10 19cm −3 were measured with mobilities ranging from 105 to 40 cm 2/V · s, respectively. SIMS data showed very abrupt profiles with no apparent memory effects. Hydrogen was also measured in the layers and annealing of samples in vacuum showed an increase in doping, of at most 50%, only for samples grown at lower temperatures, about 450°C. For most samples, however, an increase in the mobility was measured after annealing, indicating that the neutral CH complexes most likely contribute to the majority carrier scattering. Large area devices with varying base thickness, W B, and base doping, p, were fabricated. Devices showed good Gummel characteristics with n c = 1.15 and n b = 1.17. The gain variation for different devices was found to be proportional to 1 (W B p) 2 , which is consistent with a diffusive base transport and Auger-dominated recombination in the heavily doped base region. A comparison with Be-doped devices showed the same trend with slightly higher gains. It was also observed that in devices where the C-doped base was grown at temperatures 500°C the gain was shifted to much lower values. Small devices were also fabricated and measured with f T and f max values of 70 and 50 GHz, respectively.