Heterojunction laser operation of GaAs1−xPx : N on NN-pair (ENN) and A-line (EN) transitions near the direct (Γ) band edge

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Abstract
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’’.