The variation with temperature of laser threshold current density under pulsed operation conditions,Jt, has been measured for double heterostructure wafers grown with a range of values of heterojunction step height Dgr;x. Good correlation is found between Dgr;xand the temperature coefficient which is defined as the ratio of the values ofJtat 65 and 10thinsp;deg;C. Values ofJ65/J10are found to be approximately 1.5 for Dgr;x=0.30, increasing slowly to 2.0 at Dgr;x=0.20 and increasing very rapidly for smaller values fo Dgr;x. This behavior is interpreted as arising from leakage of electrons from the active region into theppassive layer. A theoretical model of carrier leakage confirms the interpretation in that quantitative agreement with experiment was obtained using reasonable values for the disposable parameters of carrier lifetime and mobility. The model is used to predict approximate limits to the Al concentrations in the passive layers needed for stable continuous laser operation over a wide temperature range.
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