Behavior of above-gap NN pair states in radiative recombination in GaAs1−xPx : N+ (x=0.24, 77°K)

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Abstract
Photoluminescence and laser data (77°K) are presented, clarifying the role of the NN pair states in above‐gap radiative transitions. Heavily Te‐doped (1019/cm3) and N‐doped (≳ 1019/cm3) x=0.24 vapor phase epitaxial GaAs1−xPx samples are prepared to ensure a large doped‐in supply of electrons in NN pairs states. Identical samples, but without N+ doping (N+‐doped layer etched off), are examined for comparison. Nitrogen‐free samples lase at energies as high as 60 meV above Eg(Γ); the N+‐doped samples lase at significantly higher threshold and at energies hv≲Eg(Γ), where resonance enhancement is large. The addition of Zn (via diffusion) to convert the n‐type N‐doped crystal to p type removes the built‐in electron supply from the NN pair states and permits laser operation on the donor band tail at relatively low energy and low threshold, which shows that the N impurity does not damage the crystal. While the N trap is most useful in GaAs1−xPx in the region near the direct‐indirect transition (x≡xc≈0.46, 77°K) and in the indirect range (x > xc), these and related data indicate that the N trap detracts from the radiative recombination process in the direct range (x≪xc).