PHOTOLUMINESCENCE ANALYSIS OF ER-DOPED GAAS UNDER HOST PHOTOEXCITATION AND DIRECT INTRA-4F-SHELL PHOTOEXCITATION

Er-doped GaAs shows a sharp and simple intra-4f-shell luminescence spe ctrum of Er3+ ions under host photoexcitation, when the crystal is gro wn with deliberate oxygen codoping by metalorganic chemical-vapor depo sition. Photoluminescence-excitation measurements by direct intra-4f-s hell excitation, however, revealed that there are many kinds of Er3+ c enters in the same crystal. To clarify the differences between these E r centers, photoluminescence was measured under both host photoexcitat ion and direct intra-4f-shell photoexcitation. It was found that there are three types of Er centers with distinctly different characteristi cs. The first type of Er center shows a sharp and simple photoluminesc ence spectrum with a high intensity under host photoexcitation. This c enter had been assigned as an Er atom coupled with two oxygen atoms (E r-Ga-20 center). The second type of Er center show sharp and simple sp ectra but only under direct intra-4f-shell photoexcitation and not und er host photoexcitation. In a sample with Er concentration of 1.4X10(1 8) cm(-3), several such centers with distinctly different atomic confi gurations were found at substantial concentrations, probably exceeding that of the Er-Ga-20 center. As there is no intra-4f-shell luminescen ce for this type of center under host photoexcitation, no energy trans fer path exists between the host and the 4f shells of this type of Er center. The third type of Er center shows complicated spectra even und er intra-4f-shell photoexcitation with a specific photon energy. Analy sis of photoluminescence spectra from this type of Er center revealed evidence of energy migration among Er3+ ions, suggesting that Er-rich aggregates are the origin of this type of PL spectra. Under host photo excitation, this type of Er center shows luminescence but with a much lower intensity than the Er-Ga-20 center. The luminescence from Er cen ters similar to the third type probably is dominant in the PL spectrum of Er-doped GaAs grown without deliberate oxygen codoping, which does not contain an appreciable concentration of the Er-Ga-20 centers. (C) 1995 American Institute of Physics.