Injection inhomogeneity and lasing thershold in III-nitride multi-QW deep-UV laser diodes

Lasing threshold conditions have been analyzed in deep-UV (DUV) multiple-QW (MQW) III-nitride laser diode (LD) structures with different QW confinement depth. Shallow QWs with smaller internal polarization fields reveal better QW emission characteristics including lower QW transparency population and higher differential gain. In MQW LD structures, however, the high-gain operation of shallow QWs is hindered by insufficient QW injection due to increased carrier leakage from shallow-QW active region. Deep active QWs can attain higher operational populations and provide for higher LD optical gain; however, LDs designed with deeper active QWs suffer from MQW population non-uniformity due to increased inhomogeneity of carrier injection. Underpumped deep QWs reduce the total modal gain of the LD structure thus deteriorating the lasing threshold and LD power conversion (wall-plug) efficiency.