Growth and device characteristics of short wavelength GaAs multiple quantum well lasers

Abstract

There is widespread interest in the use of the quantum size effect to modify the operating wavelength of semiconductor lasers, particularly in the AlGaAs/GaAs system where there is the possibility of producing short wavelength devices suitable for optical information systems. High quality current injection quantum well lasers grown by molecular beam epitaxy (MBE) have been reported with well widths as thin as 60 Å producing emission down to about 820 nm. Further reductions in wavelength have only been achieved by the addition of Al to relatively wide wells in which the wavelength shortening due to the quantum size effect is small. In this paper we report on the growth and characteristics of AlGaAs/GaAs multiple quantum well (MQW) injection lasers with thin (≤55 Å) GaAs wells utilizing the quantum size effect alone to obtain emission in the visible region of the spectrum. Growth of these multiple layer structures was carried out in a laboratory designed MBE system with rapid automatic beam shuttering in order to obtain abrupt interfaces and good periodicity. High speed substrate rotation was used to ensure uniformity across the wafer. Accurate determination of well widths is essential for meaningful comparisons between calculated and measured wavelengths, especially when well widths are reduced to a few monolayers. The well widths were determined both from growth rate, calibrated by RHEED oscillations, and by electrochemical profiling of the cladding layers. The structures were processed into oxide stripe lasers to study 300 K emission wavelengths and threshold currents as a function of well width. Laser operation at 300 K has been obtained in all devices, and a device with 13 Å wells gave the shortest wavelength (704 nm) reported for an MQW injection device with GaAs wells. The 300 K emission spectra were compared with both the calculated n=1(e‐hh) transition for each device and the wavelength of this transition obtained directly by photovoltage spectra on some devices. We have found that the lasing wavelength differs from both the calculated and measured n=1(e‐hh) transition wavelengths by about 20 nm over the whole range of well widths studied. A strong dependence of threshold currents on number of wells has been observed.