Abstract
One promising approach to cover the spectral range between 2 and 3 um, where several pollutant gases such as CO, CO2, CH4 and NH3 have strong absorption lines, is the development of GaSb-based inter-band lasers. Low-cost, continuous-wave GaSb-based vertical cavity surface emitting lasers (VCSELs) operating at ~2.4 μm up to 50°C have been demonstrated recently [1]. In this work we have used high pressure techniques to investigate ways to improve their performance and extend their working temperature range. Since the band-gap and energy of the gain peak (Ep) increase with pressure at 0.126 meV/MPa [2] at constant temperature, when applied to edge emitting lasers (EEL) we can use pressure to determine the radiative and non-radiative recombination processes occurring [3]. In VCSELs, the pressure also tunes Ep relative to the cavity mode energy Ecm, which has a much weaker pressure dependence. Figure 1 shows the pressure dependence of the threshold current, Ith, of the VCSEL at three different temperatures (−10°C, 20°C and 30°C) and of a reference EEL with the same active region (Ith in this case normalised to its value at atmospheric pressure). The decrease in Ith with increasing pressure in the EEL indicates that Auger recombination is dominant at room temperature in this materials system and explains the temperature sensitivity of these EELs [3]. In the VCSEL the pressure dependence of Ith is much more complicated. At −10°C, pressure moves Ep above Ecm and the detuning effect dominates Ith, which therefore increases. At the higher temperatures the decreasing Auger recombination initially dominates. Detailed analysis will be given, but one can immediately note that at ~130 MPa Ith is lower at 20°C and is almost stable with temperature. Therefore we predict that either increasing the band gap or increasing the operating wavelength will allow an improved temperature performance of these GaSb-based VCSELs.
© 2009 IEEE
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