New Deep-Level Luminescence in GaAs:Sn

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Abstract
A study has been made of the photoluminescence spectra of Sn‐doped GaAs grown by liquid‐phase epitaxy, in which, because of growth under As deficient conditions, compensation is expected to occur by the possible occupation by Sn atom of As sites. Hall data suggest that some compensation does take place by the formation of Sn acceptor levels. A broad emission band was found at about 1.26 eV (77°K) whose peak position follows closely the temperature‐dependent variation of the bandgap energy. This band was not seen in materials grown from the melt. It is suggested that the band is due to an acceptor 0.2±0.02 eV above the valence band edge. Evidence is inconclusive for the existence of a shallow acceptor due to Sn similar to that introduced by Si and Ge in GaAs. Thus, the deep level may be due to Sn on isolated As sites, rather than to a complex involving Sn atoms. The radiative band due to this deep acceptor exhibits unusual structure below 77°K, which is explained as an electronic transition to a tightly bound hole trapped on the deep acceptor accompanied by phonon emission. This hypothesis is consistent with other experimental observations concerning the properties of the emission band at higher temperatures. It is shown that Pb in GaAs also introduces a deep level (presumably at Ev+0.12 eV), and the resulting emission band similarly exhibits what is believed to be phonon structure.