Pseudopotential methods for superlattices: Applications to mid-infrared semiconductor lasers

Abstract

Many mid-infrared semiconductor laser sources are now being developed with superlattice active regions. Calculations of gain, index of refraction, and intervalence subband absorption for these laser materials require accurate subband energies, wave functions, and radiative matrix elements. We have recently begun using a solution method based on the empirical pseudopotential method (EPM). This method shows particular strength in analyzing structures with short periods or thin layers, for which the standard method, based on k⋅p perturbation theory and the envelope function approximation, may be problematical. We will describe the EPM applied to bulk solids and then demonstrate our direct generalization of the method for applications to superlattice structures. Calculations for recently developed mid-infrared semiconductor lasers using type-II superlattice active regions will be used to illustrate the method.

Absorbance spectroscopy and identification of valence subband transitions in type-II InAs/GaSb superlattices

“…4 However, substantial uncertainty still exists in understanding and predicting the band structure of such heterostructures. There are three interrelated reasons for this: ͑1͒ the uncertainty inherent in the growth process in controlling composition, layer thickness, and interfacial broadening can often correspond to a large difference in the resulting band structure; ͑2͒ the applicability of common band-structure calculations using the k-p envelope function approximation to model type-II heterostructures containing very thin ͑10-50 Å͒ layers may be limited; 5,6 and ͑3͒ the range of available spectroscopic data is generally too narrow to gauge the level of confidence in current theoretical calculations. In this letter, we describe the growth, structural characterization, and absorption spectroscopy of a set of InAs/ GaSb type-II superlattice samples, in which the GaSb layer thickness is systematically varied.…”

“…The EPM method used here can analyze coherently strained superlattices, and it is described fully elsewhere. 6 Briefly, the method is built upon an EPM description of the lattice potential of the binary compounds that constitute the superlattice. The effective superlattice potential is then generated by the superposition of the component pseudopotentials, and band offsets are specified at each interface.…”

“…This methodology was shown to be particularly useful in analyzing type-II SLS composed of very thin layers. 6 As the structural characterization suggests, it was assumed that the InAs-on-GaSb interface was ''GaAs-like'' and the GaSb-on-InAs interface was ''InSb-like.'' The only fitting parameter employed was the band offset, defined here as the energy separation between the GaSb valence-band edge and the InAs conduction-band edge after application of hydrostatic strain, and it was fixed at 150 meV for all the SLS samples.…”

Wavelength tuning limitations in optically pumped type-II antimonide lasers

“…The graph also shows the theoretical wavelength tuning curve calculated by a superlattice pseudopotential model ͑SEPM͒. [2][3][4] When the InAs electron quantum well thickness is set to its minimum value of 1 ML ͑Ϸ3 Å͒, the resulting low wavelength limit is near 2.5 m. Interestingly, if the electron well is completely eliminated ͑i.e., −0 ML InAs͒, the emission wavelength of the resulting epitaxy falls to ϳ2.3 m.…”

Subband transitions in dual-band n-B-n InAs/GaSb superlattice infrared photodetector identified by photoresponse spectra

“…6 The n-B-n InAs/ GaSb SLIP has already been proven to operate at a wavelength of about 8 m. 7 A thermal imager was also demonstrated by using ͓320ϫ 256͔ focal-plane-array SLIP with a cutoff wavelength of 4.2 m at a detector temperature of 77 K. 8 Owing to remarkable progress in the growth technology, the number of reports on the device achievement of InAs/ GaSb SLS has rapidly increased. [9][10][11][12][13] However, uncertainty still exists in understanding absorption and emission features of SLIPs because of diversity of SLS structures, 11,14 and the PR band selectivity in the dual-band n-B-n SLIP is a little ambiguous. In this letter, the subband transitions in MW-and LW-SLS are investigated by PR spectra and photoluminescence ͑PL͒ profiles.…”