The extreme temperature sensitivity of the threshold current, I th , above room temperature in visible edge-emitting lasers (EELs) is investigated. From measurements as a function of temperature we find that I th is dominated by the radiative current, I Rad up to $230 K so I th % I Rad as expected for an ideal device. However, above 230 K, I th increases sharply due to the onset of indirect carrier leakage which we calculate to be $20% of I th at room temperature at an emission wavelength of 672 nm. By 350 K it accounts for >70% of I th . The operating wavelength of the device can be reduced by applying pressure and then we observe that the leakage rapidly increases and at 655 nm it forms $70% of I th at room temperature. This gives rise to a significant deterioration in the light output characteristics and has important implications for producing high power EELs and VCSEL structures based upon Al(GaInP) at these shorter operating wavelengths.Effect of Indirect Carrier Leakage on Visible Al(GaInP) Lasers

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The effects of carrier leakage and gain-cavity alignment on the temperature dependence of the threshold current (I th ) in visible vertical cavity surface emitting lasers (VCSELs) are investigated. In order to assess the two effects and the degree to which they couple we have performed pressure and temperature experiments on VCSELs and their equivalent edge emitting lasers (EEL). We have established that the peak of the gain moves with pressure at a rate of 72 meV GPa À1 more than three times the rate of 22 meV GPa --1 for the cavity mode. However, we show that over the temperature operating range carrier leakage into the indirect X-minima is the major contributor to an increased I th , nevertheless optimised gain-cavity alignment can lead to more stable operation.Introduction The use of hydrostatic pressure has been an extremely useful tool for investigating Edge-Emitting-Lasers (EELs) because it provides a method of continuously varying the band gap on a single device. Changing the band gap allows us to evaluate band gap dependent processes that may affect device performance. This functional role for pressure experiments is perhaps even more invaluable when investigating multi-layered structures such as Vertical-Cavity-Surface-Emitting-Lasers (VCSELs). The less practical alternative to the use of pressure is to grow a set of devices each at a slightly different operating wavelength which would require modifying nearly all of the layers. The subsequent difference in growth quality between such structures may then obscure the underlying physics governing device performance.VCSELs operating in the 650-700 nm range have a number of potential commercial uses such as laser projection displays [1], digital versatile disk systems (DVD) and ultra fast holographic memory systems [2]. Our specific interest is their use as the light source in short haul communication networks using inexpensive plastic fibres which have an attenuation minimum at 650 nm.Devices using the GaInP/AlGaInP material system are known to have a temperature dependent threshold current (I th ) which deteriorates towards shorter wavelengths (with decreasing indium fraction) due to thermally activated non-radiative carrier leakage from the direct G-conduction band minimum into the indirect X-minima [3,4]. Measurements on EELs have shown that at room temperature the leakage current (I leak ) forms approximately 20% of the total threshold current [5]. The Distributed Bragg

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