1.55μm Efficient Temperature Insensitive GaSb-based Lasers for Telecoms Applications

Bentley, Matthew and Carrington, Peter and Krier, Anthony (2021) 1.55μm Efficient Temperature Insensitive GaSb-based Lasers for Telecoms Applications. PhD thesis, Lancaster University.

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Abstract

GaSb-based laser structures utilizing highly strained GaInSb quantum wells offer great potential for temperature insensitive emission at telecoms wavelengths (1.3 & 1.55μm) due to their intrinsic properties (CHSH Auger supressing band alignment), however until recently the development of such structures would prove impossible due to technical limitations. This work covers the study and development of GaSb-based laser structures utilizing GaInSb quantum wells with indium contents from 20%-50%, aiming to emit at 1.55μm. All samples and structures were grown at Lancaster university via molecular beam epitaxy (MBE). Transmission electron microscope (TEM) and high-resolution X-ray diffraction (XRD) were used to probe sample structure showing abrupt well-barrier interfaces, with a high degree of well homogeneity and no noticeable defects in all but the most highly strained samples, as well as good agreement between intended structure and grown structure. Initial photoluminescent (PL) test structures showed emission peaks from 1.55-1.58μm at room temperature. Laser devices grown and fabricated at Lancaster based upon earlier PL results demonstrated room temperature peak emission wavelengths between 1.58 and 1.64μm, with more highly strained (higher indium content) wells demonstrating shorter wavelengths. Photoluminescent studies showed good agreement between measured and simulated peak emission wavelengths where simulations conducted using nextnano and matlab, had been used to inform active region structural design. These studies demonstrated that at 4K and room temperature (300K) radiative recombination dominates within these structures, with Shockley-Read-Hall and Auger recombination playing less significant roles under PL conditions. Temperature and power dependant analysis of laser devices indicated characteristic temperatures of threshold current in excess of 84K and raising as high as 181K in one device at room temperature, which exceeds the general 70K room temperature characteristic temperature of threshold current for conventional devices emitting at this wavelength. Additionally, these devices did not show a decrease in characteristic temperature of threshold current as temperature increased, unlike conventional devices emitting at this wavelength. This analysis also unveiled a ~45% contribution of radiative current to threshold current at room temperature for these devices, where prior comparable structures had only demonstrated a radiative contribution of 15-40%. Total threshold current densities at room temperature varied from ~450Acm-3 in the lowest threshold device to ~900Acm-3 in the highest threshold device.