Temperature dependence of the photoluminescence of Zn-doped In0.32Ga0.68P grown on GaAs0.61P0.39 substrates

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Abstract
The photoluminescence (PL) spectra of Zn-doped In0.32Ga0.68P epitaxial layers grown on GaAs0.61P0.39 substrates by liquid-phase epitaxy has been investigated in the temperature range of 8–300 K. The radiative recombination processes of the direct In0.32Ga0.68P alloys for which the composition is near the direct–indirect band gap crossover point have been studied at various temperatures. At higher temperatures (≳150 K) only one emission band corresponding to free-electron-to-free-hole transition dominates. Two peaks and one broad band are observed in the PL spectrum when the temperature is below 100 K. The peak denoted by A is due to direct interband radiative recombination. The temperature dependence of the band gap in In0.32Ga0.68P layers can be expressed as 2.25 − [1.79 × 10−3T2/(T + 1236)] eV. The peak denoted by B, exhibited by undoped or moderately Zn-doped (p ≤ 3 × 1018 cm−3) InGaP samples, is attributed to the conduction-band-to-acceptor transition. A third broad band (C) dominates at low temperatures. The maximum shifts toward shorter wavelengths as the temperature is further lowered. It is the indirect donor–acceptor pair recombination from the unidentified deep donor levels associated with indirect Xc minima via Zn acceptor levels.