Non-square quantum well growth for reduced threshold current in tensilely strained lasers operating at 1.52m

This paper presents calculations demonstrating that non-square quantum well growth (well shaping) can result in reduced threshold current for tensilely strained quantum well bipolar diode lasers operating at 1.52im m. Calculations of subband structure, optical matrix elements and laser gain are performed for arbitrarily shaped quantum wells based on a 4-band (electron/heavyhole/ light-hole/split off-hole) Hamiltonian. For long wavelength (1.3im m to 1.55im) lasers, Auger recombination dominates the threshold current. Compared to a 1.52 mm optimal square well just below critical thickness, an InGaAs-InGaAsP (on InP) well incorporating potential ‘spikes’ and having the same wavelength can be much wider. The wider well, possible with well shaping, results in a lower value for three-dimensional (3D) carrier density at a given value of modal gain. For low loss lasers, this implies a reduction in Auger (and hence total) threshold current to a value below the best obtainable in a laser based on a square quantum well.