Electroluminescent processes in quantum well structures

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Abstract
Spectra of the electroluminescence emanating from narrow windows in the top contact stripes of GaAs/AlGaAs separate confinement heterostructure double (2*25 AA) quantum well lasers operating in the spontaneous high-injection regime have been measured as a function of the injection current. The devices have been chosen because they are of interest for the assessment of the effects of barrier size and quality upon laser performance. In this paper the integrated relative luminescence intensities from the well and barrier regions are plotted against the quasi-Fermi level separation, which has been determined from the spectra themselves; this facilitates comparisons between devices, and with calculations based on a simple model in which the carrier populations in the wells and barriers are specified by a common quasi-Fermi level. Reasonable agreement is found between the electroluminescence characteristics and theory using a carrier temperature close to that of the lattice, which indicates that electron capture into the well does not present a significant rate-limiting step in the steady-state operation of the lasers studied. Moreover, the quasi-Fermi level separations relative to the effective band gaps of the quantum wells in all the devices are found to be very similar at lasing threshold, which leads to the conclusion that differences observed in the externally measured current are largely due to non-radiative processes in the barriers or carrier leakage.