Photoluminescence of Shallow Acceptors in Epitaxial AlGaAs

The low-temperature (2 K) photoluminescence (PL) of AlxGa1-xAs (0<x<0.25 was studied in an effort to characterize shallow acceptors in material grown by organometallic vapor phase epitaxy and liquid phase epitaxy techniques. The dominant shallow acceptor in nominally undoped AlxGa1-xAs specimens grown by both techniques was identified as Carbon, with EA=26 meV for x=0. EA was observed to increase with increasing x to ~36 meV at x~0.20, as expected for an effective mass like center where EA [proportional][m*(x)/epsilon(x)2]. The PL peak due to the conduction band to acceptor transition was found to become progressively broader with increasing x, which is attributed to increasing donor plus acceptor concentration. The acceptor Ge was studied in intentionally doped LPE specimens. It also behaves as a simple effective masslike center, with EGe~40 meV for GaAs and 55 meV for Al0.2Ga0.8As, contrary to earlier reports of anomalous behavior.