The photoluminescence (PL) from GaAs/AlxGa1−xAs single and multiple quantum well (QW) heterostructures grown by molecular-beam epitaxy (MBE) has been studied in the temperature range 10<T<300 K. The temperature dependence of the PL peak energy and of the integrated intensity observed under both direct and indirect excitation of the GaAs QWs provides insight into the capture mechanism of photoexcited carriers. The temperature dependence of the QW emission energy follows the band-gap shrinkage of bulk GaAs. Deviations from this behavior are caused by lateral monolayer thickness fluctuations of the GaAs quantum well. Under direct excitation the QW luminescence intensity decreases with increasing temperature first due to a partial dissociation of excitons and finally due to thermally activated nonradiative centers. Free carriers generated in the AlxGa1−xAs barrier layers under indirect excitation diffuse rapidly into the GaAs well where they recombine radiatively. This diffusion is enhanced with the increase of temperature. A simple model allows the quantitative description of this diffusion process and of the quantum efficiency of the GaAs quantum well as a function of temperature. In the calculation of the temperature dependence of the luminescence intensity under indirect excitation we use a temperature-independent radiative recombination term and a temperature-dependent nonradiative recombination term to interpret the experimental data.

The metal-semiconductor-metal ultraviolet (UV) photodetector was fabricated on the Mg(0.47)Zn(0.53)O layer grown by radio-frequency magnetron cosputtering. The photodetector shows the peak response at 290 nm with a cutoff wavelength at 312 nm. It exhibits a very low dark current of about 3 pA at 5 V bias, and the UV-visible rejection ratio (R = 290 nm/R = 400 nm) is more than 4 orders of magnitude. The transient response for the detector was measured, and it was found that the rise time is 10 ns and the fall time is 30 ns. The reason for the short response time is related to the Schottky structure.

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