Laser and optical properties of InGaN/GaN multiple quantum well heterostructures were investigated as functions of temperature (T=80-450 K) and excitation intensity (I<sub>exc</sub>=10-1100 kW/cm<sup>2</sup>) of the N<sub>2</sub> laser radiation. Laser action was achieved in all types of the MQWs from the violet up to the blue spectral region (λ<sub>las</sub>=405-470 nm). The laser threshold at room temperature was 35-100 kW/cm<sup>2</sup> and 70-150 kW/cm<sup>2</sup> for the 'violet' and 'blue' lasers, correspondingly. The characteristic temperature in the temperature range of 80-220 K was T<sub>0</sub>=180 K for the 'violet' and T<sub>0</sub>=530 K for the 'blue' lasers. The T<sub>0</sub> was lower for all types of lasers at T>250 K. It was shown that the overheating of the active region under high excitation intensities can reach 40-100 K and it is due to inherent laser radiation.
The spectra of the optically pumped ZnMgSSe/ZnSe multiple quantum well separate confinement heterostructure lasers and the PL spectra of the heterostructures were investigated as functions of temperature (T=80-500 K), excitation intensity (I<sub>exc</sub>=0.001-1000 kW/cm<sup>2</sup>) and number of excitation pulses (N=106). The laser threshold temperature dependence was investigated and explained by alternation of the spontaneous emission efficiency and spectral broadening with temperature rise. It was shown that at room temperature the active region overheating value does not exceed 10 K at high I<sub>exc</sub>. It was established that the degradation of the heterostructures under high levels of excitation is due to the inherent laser emission interaction with the heterostructure leading to the appearance of intrinsic defects and to the inherent light stimulated interdiffusion at ZnMgSSe/ZnSe interfaces.
ZnSe/ZnMgSSe and InGaN/GaN heterostructure based lasers under optical transverse pumping by pulsed N<SUB>2</SUB>-laser radiation were investigated in a wide spectral, temperature and excitation intensity range for various types of heterostructures which differed in the epitaxial layer composition, layer sequence and thickness. The spectral- angular distribution of the laser emission of the ZnSe/ZnMgSSe separate confinement heterostructures and the influence of the excitaion intensity and the cavity length on the laser mode structure were investigated. It was found that the main degradation mechanism of the ZnSe/ZnMgSSe multiple quantum well heterostructures at temperatures higher than 400 K is the diffusion of S atoms from the barriers into the quantum wells which leads to increasing point defect concentration in the active layers of the laser. The recovery of the laser threshold of the ZnSe/ZnMgSSe MQW-SCHs degraded during thermal annealing after the action of the inherent laser radiation is attributed to a significant decrease of the point defects in the active layers. Laser action of InGaN/GaN multiple quantum well heterostructures in the blue spectral region has been obtained for the first time and investigated. Temperature tuning of InGaN/GaN MQW laser emission from the violet to blue has been realized. The influence of the photoluminescence characteristics on the laser parameters of the InGaN/GaN MQW optically pumped lasers operating in the blue spectral region is investigated.
The influence of layer thickness, heterostructure design, optical confinement factor and spontaneous emission efficiency on laser parameters of GaN based quantum well optically pumped lasers is studied in wide spectral (373 - 470 nm), temperature (77 - 600 K) and excitation intensity (10<SUP>2</SUP> - 3 10<SUP>6</SUP> W/cm<SUP>2</SUP>) regions. The laser threshold enhancement from 70 kW/cm<SUP>2</SUP> for the 421 nm operating laser to 900 kW/cm<SUP>2</SUP> for the 469.5 nm laser leads to the reduction of highest operation temperature of the laser from 585 K for the 421 nm laser to 295 K for the 469.5 nm laser with increasing operating wavelength. As a rule the far field pattern of the laser emission consists of two light spots localized at positive and negative angles of 30 - 50 degree(s). The laser spectra structure in the far-field of the SQWs and MQWs with low thickness of the active layers depended on the registration angle. The spatial distribution of the laser light in the far-field consisting of transverse and leaky modes was calculated and compared with the experimental results. Calculations of the optical confinement factor and the electromagnetic field distribution inside and outside of the heterostructures showed that the MQW lasers operate in the high order transverse mode regime. The spectral-angular distribution of the emission of the SQW and MQW lasers with low active layer thickness is due to the leaky mode formation.
We report results on the transferability of a blue-green electroluminescence test structure (ELT) process across different reactor geometries and substrate materials. The process was transferred from the conditions of our well-known 6 X 2 inch to the 5 X 3 inch AIX 2400 G3 geometry by simple up-scaling of the respective process parameters in accordance with numerical simulations done on the reactor setup. The five period InGaN/GaN quantum well ELT structures with an average emission wavelength on wafer of 480 nm shows a standard deviation of 1 - 2% without rim exclusion. Electroluminescence up to 560 nm were achieved in InGaN/GaN structures with high In content. With these prospects new types of seed layers for the transfer of our standard electroluminescence test structures (ELT) process to Si- substrates were investigated. The growth on different seed layers was found feasible and resulted in operational ELT structures with emission wavelengths in the range of 440 nm to 470 nm. Electrical quick test shows bright blue emission across the full Si wafer.