Heterojunction laser operation of N-free and N-doped GaAs/sub 1-y/P/sub y/ (y=0.42--0.43, lambdaapprox.6200 A, 77 degreeK) near the direct-indirect transition (yapprox.y/subc/approx. =0.46)

Single heterojunction diodes constructed by the LPE growth of In1−yGayP1−zAsz on otherwise identical N-free and N-doped VPE GaAs1−xPx substrates permit the examination of laser operation on NN-pair (ENN) and A-line (EN) recombination transitions near the direct (Γ) band edge of GaAs1−xPx. Data are presented on the effect of NN-pair states on laser operation in the region ‖EΓ−ENN‖≲50 meV (ENN<EΓ, x?0. 32), where NN-pair states are degenerate with a large donor band tail (nd?1. 6×1018/cm3). The NN-pair states cause increased laser threshold current density, increased laser photon energy, and a large effective index [n−λ (dn/dλ)]≳5 that is free of structure. Photoexcitation data on thin p-type platelets prepared from the same substrate crystal are described confirming this behavior. Data are presented also for the case of single N atom (A-line) states lying below EΓ and degenerate with donor tail states in GaAs1−xPx : N (x?0. 40). The laser threshold current is increased because of the N doping, as for NN-pair states, but recombination on the A line occurs at lower energy (EN<EΓ) than for otherwise identical N-free diodes, which automatically operate as lasers at high thresholds and photon energies hν∼EΓ. In addition, the presence of N-trap states in the region of donor tail states results in the observation of structure (4. 2 °K) in the index dispersion [n-λ (dn/dλ)] in the spectral region of the A line. This behavior is attributed to the resonant-antiresonant properties of a narrow autoionizing trap state (N trap) located in the donor tail state ''continuum''.