AbstractsAstronomy & Space Science

We present new insights into the problem of the isoelectronic nitrogen (N) impurity in gallium arsenide (GaAs). By performing photoluminescence (PL), photoluminescence excitation (PLE), transmission, and time decay measurements through a broad range of pressures, we were able to positively identify and track previously unseen states arising from the N impurity.;The first observation we make is of a dramatic increase in luminescence as N forms an isolated state within the gap around 22kbar. We attribute this effect to N acting as a nonradiative trapping center while still resonant with the conduction band states. We also note the appearance, above 22kbar, of a broad band-to-acceptor like emission below the band edge, which we associate with a band to N acceptor transition.;The next major observation we report is of the excited state of the N x exciton. We find this state to be clearly identifiable for the pressure range ~25kbar to ~30kbar, and is weak in PL, but shows enormous absorption signals in PLE and transmission. The spacing of this level from Nx-B is in good agreement with the established theory of shallow acceptor levels.;We then move on to the identification of a second bound state associated with N. This state, designated NGamma, was previously reported for the GaP system and the GaAs1-xPx alloy, but has not, until now, been positively identified in GaAs. We find the state to be degenerate with the shallow donor level for pressures up to ~30kbar. The emission from this state is found to possess unique N characteristics and is seen to move in pressure with both shallow and deep like properties.;We conclude with a discussion of the process of lasing in N doped GaAs. We present data consistent with previous studies of the lasing process in GaAs. However, we find an intriguing trend with pressure as we approach the Gamma-X crossover. The lasing gain begins to shift in a manner similar to NGamma . In fact, NGamma appears to act as an upper bound on the laser emission. We believe this to be preliminary evidence of the influence of N on the lasing mechanism.