Luminescence and direct experimental observations of band-structure effects in nitrogen-doped GaxIn1−xP alloys

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Abstract
Undoped and nitrogen‐doped GaxIn1−xP layers (0.87<xxIn1−xP films is reported as a function of the NH3 partial pressure in the tube during the growth process. Photoluminescence spectra (4.2 °K) show a net change before and after the nitrogen doping. In undoped samples, a sharp high‐energy C line due to excitons bound to neutral donors dominates the spectrum, while in nitrogen‐doped samples additional lines appear with features depending on the composition. Particularly, we observe that, for x≳0.98, the nitrogen line is similar to the A line observed in GaP, whereas for xAo at lower energy than A. The origin of these recombinations is studied by time‐resolved spectroscopy in undoped or nitrogen‐doped materials. In undoped layers, the fast luminescence decay (20 ns) confirms the origin of the C line. For nitrogen‐doped samples, we show that the measured luminescence decay time is the radiative lifetime τxR of the nitrogen‐bound exciton. This lifetime decreases when the GaP content in the alloys decreases, i.e., when the X conduction band comes closer to the Γ conduction band. The experimental variation of τxR agrees with a simple theoretical model involving only the three minima Γ, X, and L and also with the more sophisticated model of Holonyak. Such a variation is a direct experimental observation of the band‐structure effect.