Effects of quantum well design on the optical and microwave performance of strained-layer GaInAs/GaAs lasers

By introducing strain into semiconductor lasers using GaAs/Gai-xlnxAs quantum wells, their modulation bandwidth has been increased to beyond 20 GHz1'2'3& Our approach to high modulation bandwidth strained layer quantum well lasers has been to fabricate short cavity (less than 1OO.tm) multiple quantum well structures. In order to fabricate lasers of this length, the facets must be etched by chemically assisted ion beam etching (CAIBE) and not by cleaving. In short cavity, multiple strained quantum well lasers fabricated by CAIBE, it has recently been shown using two different layer structures5'6 that a 3dB modulation bandwidth of 28 GHz is obtainable under cw conditions. The current study investigates three issues in the fabrication of strained layer quantum well lasers for high speed operation (1) the growth of different quantum well and barrier materials and their effects on device performance, (2) the dependence of differential gain and damping on quantum well width, depth, and number, and (3) the relationship between threshold current (th) and high speed performance. Wafers have been grown with indium contents from 20 -40%, well widths from 30 70A, and from two to five quantum wells. From the results on these wafers, some design criteria for optimizing high-speed performance will be presented.