Electroluminescence spectra from In 1- x Ga x P p - n junctions have been measured at 77 K and at higher temperatures for a number of diodese with x =0.5 to 0.9, in particular, near the crossover composition. Various peaks appear in the spectra as the forward current increases from 10 -3 A/cm 2 to 30 A/cm 2 . The current dependence of the spectra is studied in detail. The spectra and their temperature dependences in the direct-band-gap region are found to be greatly different from those in the indirect-band-gap region. In the direct-band-gap region, four peaks P 1 , P 2 , P 3 and P 4 are usually observed at 77 K. The highest-energy peak P 1 is 0 to 20 meV below the Γ conduction band which has been estimated from the 300 K cathodoluminescence. The energy separation between P 1 and P 3 is 70–75 meV. In the indirect-band-gap region, two weak bands A 1 and A 2 are observed on the higher energy side of the dominant band P 1 due to the donor-acceptor transition at 77 K. The energy position of the highest energy peak A 1 is very near the expected energy position of the free exciton of excitons trapped by some shallow impurities. At 177 K, A 1 and A 2 become dominant compared to P 1 . The cross-over composition of direct- and indirect-band-gaps is estimated to be close to 0.72.
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Okuno et al. (1975) studied this question.