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Long-wavelength vertical cavity surface emitting lasers (VCSELs) operating in the 1 .3tm to 1 .5im wavelength range are ideal light sources for optical fibre communication applications. However, a number of problems have hindered progress in the development of cost-effective long wavelength VCSELs. These are (a) inthnsically high non-radiative losses, (b) difficulty in fabricating highly reflecting mirrors, lattice-matched to InP, and (c) the disparity between the predicted and observed temperature dependence of the operation of the devices. In this report we present the results of our studies concerning the pulsed operation of a bulk GaInAsP/InP VCSEL fabricated at BT laboratories. The device is tailored to emit at around 1 .5 im at room temperature. The structure has a 45 period n-doped GaInAsPIInP bottom Distributed Bragg Reflector (DBR), and a 4 period Si/A1203 dielectric top reflector. Spectral electroluminescence (EL) from a 16 im diameter window is measured in the pulsed injection mode. Device parameters are recorded in the temperature range between 90 K and 240K. Threshold current exhibits an approximate parabolic temperature dependence with a broad minimum of J = 13.2 kA cm2, at temperatures between 170K and 195K. Temperature dependence of the threshold current is compared with the theoretical calculations which consider radiative transitions with and without k-selection. Best agreement with the experimental results is obtained when a partial k-selection model, with an energy broadening of about 4.4 meV, is used in the calculations.

The hot Electron Light Emission and Lasing in Semiconductor Heterostructure devices (HELLISH-i) is novel surface emitter consisting of a GaAs quantum well (QW), within the depletion region, on the n side of GaiA1As p-n junction. It utilises hot electron transport parallel to the layers and injection of hot electron hole pairs into the quantum well through a combination of mechanisms including tunnelling, thermionic emission and diffusion of lucky' carriers. Super Radiant HELLISH-i is an advanced structure incorporating a lower distributed Bragg reflector (DBR). Combined with the finite reflectivity of the upper semiconductor-air interface reflectivity it defines a quasi-resonant cavity enabling emission output from the top surface with a higher spectral purity. The output power has increased by two orders of magnitude and reduced the full width at half maximum (FWHM) to 2Onm. An upper DBR added to the structure defines HELLISH-VCSEL which is currently the first operational hot electron surface emitting laser and lases at room temperature with a l.5nm FWHM. In this work we demonstrate and compare the operation of UB-HELLISH-l and HELLISH-VCSEL using experimental and theoretical reflectivity spectra over an extensive temperature range.