Influence of leakage and gain-cavity alignment on the performance of Al(GaInP) visible vertical-cavity surface emitting lasers

The temperature dependence of the threshold current I_th in visible vertical-cavity surface emitting lasers (VCSELs) is investigated. To separate the intrinsic, material effects such as carrier leakage into the X-minima from the structurally induced gain-cavity alignment effects of the VCSEL structure, simple equivalent edge emitting lasers (EELs) are considered in conjunction with full VCSELs. From measurements as a function of temperature and pressure, it is deduced that carrier leakage accounts for approximately 20% of I_th at room temperature, increasing strongly with an activation energy of 267 meV. Measurements performed on full VCSEL structures containing the same active region as the EELs show similar behaviour around room temperature, clearly indicating that under normal operating conditions the temperature dependence of the VCSELs is also dominated by carrier leakage. At higher temperatures, carrier leakage coupled with gain-cavity detuning gives rise to a further increase in I _th. The effect of detuning at low temperatures (<200 K) is also observed, where I_th again increases for the VCSEL. Interestingly, while the maximum output power of the VCSEL strongly decreases at elevated temperatures, it shows no such decrease at the lowest temperatures, confirming that carrier leakage also limits the maximum power output of visible VCSELs