We have measured electroluminescence (EL) spectra of GaAs/InGaAs and AlGaAs/GaAs single quantum well (QW) p-i-n photodiodes at temperatures between 200 and 300 K and forward biases close to the open circuit voltage. Integrated EL spectra vary like eqV/nkT with an ideality factor n=1.05±0.05 over five decades, indicating purely radiative processes. The spectra are calibrated into absolute units enabling comparison to be made with the predictions of a theoretical model. For each temperature and bias we calculate the EL spectrum and radiative current expected in the detailed balance limit, integrating the theoretical emission spectrum over the surface of the device, in order to establish the quasi-Fermi potential separation, Δφf, in the QW and, where possible, in the host material. For the GaAs/InGaAs cell we are able to model emission from the QW and the host material simultaneously. We find that, in all cases, the QW emission is overestimated by theory if it is assumed that Δφf=V. QW emission corresponds instead to a value of Δφf which a few tens of mV less than V. In contrast, emission from the host material, where visible, is well fitted by the model with Δφf=V at all biases and temperatures. We attribute the variation in Δφf to irreversible thermally assisted escape from the QWs.

No abstract

No abstract

No abstract

The effect of the dislocation line density produced by the relaxation of strain in GaAs/In x Ga 1Ϫx As multiquantum wells where xϭ0.155-0.23 has been studied. There is a strong correlation between the dark line density, observed by cathodoluminescence, before processing of the wafers into photodiode devices, and the subsequent low forward bias ͑Ͻ1.5 V͒ dark current densities of the devices. A comparison is made of the correlation between the reverse bias current density and dark line density and it is found that, in this range of strain, the forward bias current density varies more. Two growth methods, molecular beam epitaxy and metal organic vapor phase epitaxy, have been used to produce the wafers and no difference between the growth methods has been found in dark line or current density variations with strain.