This paper describes the characteristics of a separate confinement heterostructure laser design based on type-I
InAsSbP/InAsSb multiple quantum wells (MQW). An 8×8 band k.p method was used to calculate the band structure.
The optical gain of the active region containing InAsSb QW was calculated using a free carrier gain model. Other
properties such as behavior of the fundamental optical TE mode and refractive index profile were also determined. These
were used for simulation of the resulting device properties and to estimate the threshold modal gain and threshold current
density for the InAsSb MQW laser. Suitable InAsSbP cladding layer and waveguide/barrier materials have been
determined. The strain, critical thickness, band offset, optical gain, Auger coefficient and threshold current density have
been calculated at various Sb contents (x). The lowest current density is found for the composition range between
0.12<x<0.16, where the estimated laser threshold current density is 1.85-1.86 kA cm<sup>-2</sup>.
In this work we report on a specially optimized type-I InAsSb/InAsSbP double heterostructure (DH) ridge laser grown by liquid phase epitaxy (LPE). To remove residual impurities and reduce Shockley-Read recombination, the active region was purified using a Gd gettering technique. In addition free carrier absorption loss was minimized by the introduction of two undoped quaternary layers with the same composition of the cladding layers either side of the active region. The inserted layers also helped alleviate inter-diffusion of unwanted dopants towards the active region during or after growth and reduced current leakage of the device. The diode lasers operate readily in pulsed mode at elevated temperatures and emit near 3.45 μm at 170 K with a threshold current density as low as 118 A/cm<sup>2</sup> at 85 K. Compared to the conventional 3-layer DH laser, the optimized 5-layer structure with reduced optical loss can raise the maximum lasing temperature by 95 K to ~210 K.
We report on the liquid phase epitaxy (LPE) growth of an optimized double heterostructure (DH) 3-4 μm laser and the use of linear rapid slider boat technology for the production of quantum well (QW) structures based on InAsSb/InAsSbP. Typical characteristics of some of these prototype sources are presented and analyzed, including the results of SEM, X-ray diffraction, photo- and electro-luminescence characteristics of prototype DH & QW devices. The optimized 5 epi-layer diode lasers operate readily in pulsed mode at elevated temperatures and emit near 3.45 μm at 170 K with a threshold current density as low as 118 A/cm<sup>2</sup> at 85 K. Coherent emission was obtained up to 210 K. LPE growth of InAsSb QW has been successfully obtained experimentally. The QW structure has been confirmed by SEM and electroluminescence measurements at different temperatures.
The upconversion fluorescence was recorded at room temperature and investigated in LiKGdF5: 2%Er<sup>3+</sup>, 0.4%Tb<sup>3+</sup> single crystal grown by the hydrothermal synthesis technique under 514.5 nm and 785 nm laser excitation, respectively. Under 514.5 nm laser excitation, four strong upconverted emission bands with peaks at 410 nm (violet), 470 nm, 486 nm and 492 nm (blue) were obtained. The former two emission bands were assigned to be corresponding to <sup>2</sup>H<sub>9/2</sub> -> <sup>4</sup>I<sub>15/2</sub> and <sup>2</sup>P<sub>3/2</sub> -> <sup>4</sup>I<sub>11/2</sub> transitions of Er<sup>3+</sup> ions, and the latter two are possibly corresponding to <sup>5</sup>D<sub>4</sub> -> <sup>7</sup>F<sub>6</sub> of Tb<sup>3+</sup> and <sup>4</sup>F<sub>7/2</sub> -> <sup>4</sup>I<sub>15/2</sub> of Er<sup>3+</sup>. The power dependence for 410 nm and 470 nm indicates that they arose from two-photon upconversion processes. While for 486 nm and 492 nm emission, the logarithmic slope is 0.98, which was explained by mutiphonon assisted upconversion process and energy transfer from <sup>4</sup>F<sub>7/2</sub> (Er<sup>3+</sup>) to <sup>5</sup>D<sub>4</sub> (Tb<sup>3+</sup>). Under 785 nm laser excitation, besides four weak upconverted emissions mentioned above, three strong emissions with peaks at 523 nm (<sup>2</sup>H<sub>11/2</sub> -> <sup>4</sup>I<sub>15/2</sub>), 550 nm ( <sup>4</sup>S<sub>3/2</sub> -> <sup>4</sup>I<sub>15/2</sub>) and 660 nm (<sup>4</sup>F<sub>9/2</sub> -> <sup>4</sup>I<sub>15/2</sub>) were also observed. The possible upconversion mechanism for these seven emissions was all given with the help of the power dependence of upconversion emission intensity and the energy level diagram of Er<sup>3+</sup> ions.