High CW conversion efficiency in a strained InGaAs/AlGaAs quantum well laser (λ = 930nm)

Abstract

A strained InGaAs/AlGaAs quantum well laser with a front-end power conversion efficiency exceeding 33%, and available output power greater than 1 Watt, is demonstrated. The laser structure is grown by atmospheric pressure organometallic vapor phase epitaxy, and consists of a graded index separate confinement heterostructure (GRIN SCH) with a 70Å In0.2Ga0.8As strained quantum well active region. The lasing wavelength of 930nm is in good agreement with that expected from quantum well thickness and composition. The longest attainable wavelength is dictated by the tradeoff between InAs alloy content and sub-critical quantum well thickness; we have fabricated devices up to λ = 1.08μm. Threshold currents of strained quantum well lasers are as low as those in unstrained lasers. In fact, they may be lower, a result of some beneficial effects of biaxial compression, and the possibility of higher confinement factors. Despite this, quantum efficiencies are somewhat reduced; the best we have observed is ηe = 58.4%. This may be due to the increased importance of nonradiative processes in the low-bandgap InGaAs. With the exception of lower quantum efficiencies, these devices behave much like unstrained GaAs quantum well lasers. For example, in the short-cavity regime, where average losses are high, threshold currents are increased while characteristic temperatures decrease.