Self-heating effects in red (665 nm) VCSELs

The threshold current (I_th) of GaInP/AlGaInP based vertical cavity surface emitting lasers (VCSELs) is very sensitive to temperature. The extent to which self-heating in a compact VCSEL structure couples with temperature sensitive loss mechanisms is investigated. In particular, the authors consider the strong increase in threshold current (I_th) due to carrier leakage into the X-minima and gain-cavity detuning effects. They find, using two experimental methods and from a thermal model, that the current-induced increase of the active region temperature (ΔT) increases linearly with I_th at a rate of ~14.5 K mA^-1 over a limited substrate temperature range. They estimate that the additional losses due to self-heating rise from 5% of the total I_th at room temperature (20°C) to 30% at 47°C. To uncouple the effects of leakage and gain-cavity alignment, they have calculated the gain spectra to find the radiative current as a function of temperature. They thus verify that leakage coupled to self-heating is the major cause of the increase in I_th in these devices at room temperature and above. Gain-cavity detuning has minimal effect on I_th due to the broad short wavelength tail of the quantum well gain spectrum