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In the literature, theoretical studies have indicated the quantisation of optical modes by cavity confinement may lead to enhancement of spontaneous emission factor β. Placement of a radiating system within a cavity with a dimension the order of one wavelength alters the number of allowed optical modes to which photons couple. However, this does not guarantee enhancement. A typical semiconductor laser will be required to operate over a temperature range of at least 80 o C. Here we model the confinement of a radiating source between two DBR mirrors forming a planar microcavity and consider β as a function of temperature where we use a calculated temperature dependent emission line, which the authors believe to be the first investigation including cavity effects. The results show that at threshold β has a broad maximum with increasing temperature.

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.

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