Temperature sensitivity of the threshold current of long-wavelength InGaAs-GaAs VCSELs with large gain-cavity detuning

Record-long emission wavelengths up to 1.3 μm have recently been demonstrated from highly strained InGaAs-GaAs double-quantum-well (DQW) vertical-cavity surface-emitting lasers (VCSELs). The operation of InGaAs VCSELs at such long wavelengths has relied on a large detuning between the spectral positions of QW gain maximum and cavity resonance. This detuning also affects the high-temperature performance and temperature sensitivity of such devices. In this paper, we present and evaluate the threshold current-temperature characteristic of such lasers in relation to the gain-cavity detuning at room temperature (RT). For a near-zero gain peak offset from the emission wavelength at RT, the minimum threshold current is found at the temperature where the gain peak wavelength and the cavity resonance are approximately aligned. This is well in line with a common design rule for GaAs-based VCSELs. However, we show that this design rule fails in the case of larger gain-cavity misalignment at RT. Instead, a minimum threshold current is obtained considerably below the temperature of zero gain offset. We propose a conceptual model that relates the gain-cavity detuning at RT to the temperature sensitivity of the active region performance, which qualitatively describes the threshold current-temperature characteristic typical of VCSELs. The results demonstrate the importance of improving the temperature characteristic of the active region in order to reduce the high temperature sensitivity of devices with large detuning.