Optimization of optical characteristics of a strained nitride semiconductor based quantum well laser

Abstract

In this work, a wurtzite-strained nitride based single quantum well laser structure has been designed using a 12Å InN well layer and 15Å In0.25Ga0.75N barrier layer which is characterized and optimized for an optical output of 1330nm wavelength known for short distance communication. A Separate Confinement Heterostructure (SCH) layer of GaN has been used for providing better confinement for carrier and photon. Materials and device parameters are selected using practical considerations for fabrication process. A self-consistent Schrodinger Solver along with a simulation model for obtaining optical properties has been developed for the characterization which is verified with previously published work. In self-consistent Schrodinger solver, two Schrodinger equations for both conduction and valence band have been solved followed by the performance of Poisson’s equation. The 6-band k.p formalism has been utilized for valence band calculation including valence band mixing, strain effect, spontaneous polarization, and piezoelectric polarization effect, etc. With the performed energy subbands, interband transition momentum matrix elements are calculated. Several optical characteristics like spontaneous emission rate, material gain, radiative recombination current density etc. are performed from the obtained electronic properties. Also parameters like, peak material gain versus carrier density and material gain versus radiative recombination current density are found out to characterize the structure. At carrier density of 6×1019 cm-3 and T = 300K, the peak optical gain of 5261.5187 cm-1 has been found at emission wavelength of 1336.7 nm. The peak spontaneous emission rate per energy interval per volume is 7.21×1027 s-1cm-3eV-1 at 1329.55 nm wavelength. Later, a genetic algorithm based optimization process has been performed to obtain the maximum spontaneous emission rate and maximum optical gain for the structure taking well width, barrier width, injection carrier density and SCH width are taken as variables into consideration. From the characterization, it has been found that the device will provide good amplification for TEpolarization light. This structure shows a good amount of spontaneous emission rate for lasing action with respect to the other structures published previously. Moreover, it shows a good improvement of material gain which will provide better LED and LASER action. A higher differential gain has been found for this structure which will provide higher modulation bandwidth and lower frequency chirp. Besides, the structure shows good amount of optical gain with respect to recombination current density. All these performances make this structure promising for LASER application at around 1330nm emission wavelength.