LOW-THRESHOLD-CURRENT-DENSITY 1.5-MU-M LASERS USING COMPRESSIVELY STRAINED INGAASP QUANTUM-WELLS

A low-threshold-current-density (J(th)) of 140 A/cm2 for broad-area 1.5-mu-m semiconductor lasers with uncoated facets is demonstrated at a cavity length of 3.5 mm. This was achieved by the use of a single InGaAsP quantum well (QW) of 1.8% compressive strain inside a step-graded InGaAsP waveguide region. Low-cavity losses of 3.5 cm-1 and a relatively wide quantum well as compared to InGaAs wells of equivalent strain contribute to this high performance. Double QW devices of 2 mm length showed threshold current densities of 241 A/cm2. Quaternary single and double QW's of similar width but only 0.9% strain gave slightly higher threshold current density values, but allowed growth of a 4 QW structure with a J(th) of 324 A/cm2 at L = 1.5 mm.