Narrow Results

Recent progress and state of GaSb based type-I lasers emitting in spectral range from 2 to 3.5 μm is reviewed. For lasers emitting near 2 μm an optimization of waveguide core width and asymmetry allowed reduction of far field divergence angle down to 40-50 degrees which is important for improving coupling efficiency to optical fiber. As emission wavelength increases laser characteristics degrade due to insufficient hole confinement, increased Auger recombination and deteriorated transport through the waveguide layer. While Auger recombination is thought to be an ultimate limiting factor to the performance of these narrow bandgap interband lasers we demonstrate that continuous improvements in laser characteristics are still possible by increasing hole confinement and optimizing transport properties of the waveguide layer. We achieved 190, 170 and 50 mW of maximum CW power at 3.1, 3.2 and 3.32 μm wavelengths respectively. These are the highest CW powers reported to date in this spectral range and constitute 2.5-fold improvement compared to previously reported devices.

A novel approach for cascade diode lasers was developed based on type-I quantum wells (QWs). This design adopted the leaky window effect in the GaSb/InAs band alignment for cascade pumping, and exploits the carriers recycling by the cascade pumping and the high optical gain of the type-I QWs. Two-stage cascade lasers were designed and fabricated for 2.45 and 3.0 μm, demonstrating twofold improvement in the internal efficiency. Record continuous-wave (CW) output power of 1.2 W for 2.45 um and 590 mW for 3.0 um were achieved in room temperature (RT), and the devices operate with higher power conversion efficiency at high power level, compared to conventional single-stage diode lasers.

The interesting problem of the first phase transition which is induced by pressure in AlSb and GaSb antimonide binaries is revisited. Then, the case of the AlGaSb ternary has been investigated too. The choice of ternary AlGaSb is due to the particular attention which is given actually to it and to the quasi-absence of investigations of the phase transitions in it. We found that low pressures applied to GaSb and AlSb induce transitions from zinc-blende to Imm2 and from zinc-blende to Cmcm, respectively. Our result for AlSb is in agreement with literature, and in the case of GaSb which poses the problem, we find that the Imm2 phase presents a lower total energy than the b-β-Sn phase. For ternaries, the transition is found to be to a phase which is obtained from the Cmcm phases of binaries. Calculations were performed using the plane wave version of the FPLMTO (PLW-FPLMTO) first principle method based on the local density approximation (LDA) and the generalized gradient approximation (GGA96).

Understanding the behavior of excess Ga is important for fabrication methods that employ the sputtering of GaSb-based materials. This is due to the comparatively low vapor pressure of Ga, which can result in GaSb becoming Ga-rich under experimental conditions. In this study, the growth and characterization of nonstoichiometric polycrystalline GaSb thin films with excess Ga, grown by RF magnetron sputtering, are reported. Ga content was adjusted by mixing N₂ in the Ar sputtering gas. The structural properties indicate that the grown thin films maintain the zinc blend structure of GaSb, and have an induced tensile strain along a direction parallel to the substrate. Excess Ga segregates towards the film surface and forms micro/nanoclusters. The internal tensile strain and the Ga cluster formation have little effect on the intrinsic properties of GaSb. These findings could lead to the fabrication of GaSb-based thin films using sputtering with excellent mass productivity.

Gallium antimonide (GaSb)-based devices operate efficiently in the infrared region. Investigating the toxicity of GaSb thin film is necessary for using embedded GaSb-based devices in living organisms. In this study, viability, oxidative stress, inflammatory responses, apoptosis induction and genotoxicity of GaSb were assayed using L929 cells following a 24 h exposure to GaSb. GaSb thin films were deposited on a quartz substrate using radio frequency (RF) magnetron sputtering. These films were soaked in cell culture medium to prepare test solutions. The viability of cells treated with the GaSb extract was lower than that of control cells. GaSb elicited little reactive oxygen species (ROS) generation. Tumor necrosis factor (TNF)-$\alpha$ and interleukin (IL)-1$\beta$ levels were elevated in GaSb-treated cell culture supernatants. Apoptosis and genotoxicity were not evident following GaSb treatment. Overall, these results demonstrate the low toxicity of GaSb compared with previous studies examining arsenic-containing III–V materials, which is desirable for biological devices.

Proton-irradiation induced defects in Te-doped GaSb have been studied by photoluminescence (PL) and positron annihilation spectroscopy (PAS). A 2.6 MeV proton irradiation with fluences of 1×10¹⁴ cm^-2, and 3×10¹⁵ cm^-2 was used to produce defects in the Te-doped GaSb samples with free electron concentration of 1×10¹⁷ cm^-3 and 1×10¹⁸ cm^-3 respectively. The change of S parameters in Te-doped samples irradiated with different proton fluences, indicates that the defects induced by proton irradiation are most likely the V_Ga-related defects. The PL spectra of Te-doped GaSb with different proton irradiation doses were measured at 77 K. The results show that the V_Ga-related defects induced by proton irradiation are acceptors in Te-doped GaSb. We have also found that the dopant-induced vacancies which are related to Te have existed in unirradiated samples.

A novel approach for cascade diode lasers was developed based on type-I quantum wells (QWs). This design adopted the leaky window effect in the GaSb/InAs band alignment for cascade pumping, and exploits the carriers recycling by the cascade pumping and the high optical gain of the type-I QWs. Two-stage cascade lasers were designed and fabricated for 2.45 and 3.0 μm, demonstrating twofold improvement in the internal efficiency. Record continuous-wave (CW) output power of 1.2 W for 2.45 um and 590 mW for 3.0 um were achieved in room temperature (RT), and the devices operate with higher power conversion efficiency at high power level, compared to conventional single-stage diode lasers.