EXCITON-TRANSITIONS AND PHOTOVOLTAIC SPECTRA IN GAAS/ALGAAS MULTIPLE QUANTUM-WELLS

The photovoltaic spectra of GaAs p-i-n diodes in which the insulating region contained several molecular beam epitaxy quantum wells of nominally undoped GaAs with AlGaAs barriers were studied as a function of temperature in the interval 10-300 K. To understand the effect of the transport mechanism of photoexcited carriers on the photovoltaic response, the temperature dependence of the absorption and photovoltage peaks was measured together with the enhancement of heavy-hole electron (n = 1) exciton resonance over a wide temperature range. The temperature dependence of the lineshapes of photovoltaic and absorption spectra showed comparable thermally activated broadening, and the strength of the absorption signal increased with decreasing temperature, giving a nearly constant integrated area. The intensity of the photovoltaic peaks showed non-monotonic behaviour with a minimum at about 100 K. This was tentatively attributed to the temperature dependence of the dark current-voltage characteristics of the diode and the exciton lifetime.