Growth and Electronic Properties of GaAsN and GaAsBi Alloys.

[摘要] Dilute nitride and dilute bismuthide semiconductor alloys are of significant interest since their bandgap energies can be tuned dramatically without a substantial change in lattice parameter, making them promising for a wide variety of optoelectronic applications. We examine the role of N environment on persistent photoconductivity (PPC) in GaAsN films. For N fractions >0.006, significant PPC is observed at cryogenic temperatures, with the PPC magnitude increasing with increasing N fraction due to an increase in the density of N-induced levels. Interestingly, rapid-thermal annealing suppresses the PPC magnitude and reduces the N interstitial fraction; thus, the N-induced level is likely associated with N interstitials. PPC is attributed to the photogeneration of carriers from N-induced levels to the conduction-band edge, leading to a modified N molecular bond configuration. With the addition of thermal energy, the ground state configuration is restored; the N-induced level is then able to accept carriers and the conductivity decays to its preillumination value.Furthermore, we have used PPC to drive a metal-insulator transition in GaAsN, allowing us to extract the electron effective mass using the Mott criterion.Reports indicate that the effective mass of GaAsN is dopant-dependent.We find that the effective mass for Si-doped GaAsN is consistent with predictions considering N clustering. For molecular-beam epitaxy of GaAsBi, we show that Bi incorporation into GaAs is favorable over a wider range of growth conditions with As_4 in comparison with As_2, facilitating growth of smooth, droplet-free GaAsBi films.The preference for Bi incorporation with As_4 is associated with the differences in the likelihood for As_2 vs. As_4 to replace weakly bonded surface Bi_2.Then, we consider the role of the transition from Group-V-rich to Group-III-rich conditions (the stoichiometry threshold) on the negative or positive type conductivity induced by silicon incorporation.For As-rich GaAsBi growth, Si incorporation leads to n-type conductivity. For Ga-rich GaAsBi growth, GaAsBi:Si films are p-type, and free carrier concentrations in excess of 5x10^{18} cm^{-3} are achieved for Bi fractions ~0.05, making Si a promising acceptor dopant.We propose a dopant incorporation mechanism based upon the growth-rate dependence of the stoichiometry threshold for GaAsBi.

[发布机构] University of Michigan

[效力级别] GaAsBi

[关键词] GaAsN;GaAsBi;persistent photoconductivity;effective mass;stoichiometry;doping type;Physics;Science;Physics