Anomalous length dependence of threshold for thin quantum well AlGaAs diode lasers

The threshold current in conventional semiconductor diode lasers decreases linearly with decreasing cavity length. We have found that for AlGaAs diode lasers fabricated from very thin active layer material, the threshold current can be essentially constant over a wide range of cavity lengths. At short cavity lengths, threshold increases dramatically. This anaomalous behaviour is attributed to physical mechanisms which become important when active layer threshold gain requirements become unusually high.