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A distinctive method is used to achieve transverse-mode control by building and integrating a tunable liquid crystal (LC) mode filter on top of traditional vertical-cavity surface-emitting lasers (VCSELs). An LC cell is fabricated by injecting a type of nematic LC material (E7) in an annular groove patterned by SiO2. By electrically tuning the refractive index of the LC, a spatially dependent reflectivity profile can be achieved and optimized, which directly influences the threshold modal gain of each transverse mode provided by oxide-confined VCSELs. The flexible and accurate control performance of the LC mode filter structure have been demonstrated by the simulation results and our analysis. This design is a completely novel method to realize VCSELs with an accurate and real-time controllable transverse-mode, and it will probably play a significant role in the future. [ABSTRACT FROM AUTHOR]

The lateral wet-etching kinetics of an Al0.8Ga0.2As sacrificial layer, a typical configuration for optoelectronic devices, has been investigated in detail. Expanding the one-dimensional Si and AlAs oxidation modes to the Al0.8Ga0.2As sacrificial layer etching process, compact analytical formulas were obtained for the time evolution of the etch front and for the etch rate. Through both experiment and theoretical calculations, the lateral etching process parameters, A, B, and B/A, have been obtained for the different temperatures and etchant volume ratios. The etch rate is found to remain almost constant for a large range of etch length. However, when the etch temperature increases, a rapid increase in this rate is predicted. Activation energies for the process parameters, EA∼0.1 eV and EB∼0.5 eV, have also been obtained for the etchant volume ratio of 3:1 and the sacrificial layer thickness is 800 nm. [ABSTRACT FROM AUTHOR]

p-GaAs/n-GaN heterojunction was fabricated by wafer bonding. Its current-voltage characteristic was systematically investigated at room temperature and at a variety of low temperature. The curves of different temperatures in the logarithmic scales indicate space-charge-limited currents (SCLCs) in the high voltage region (>0.4 V). SCLC current-transport mechanism was confirmed by fitting data. Single-charge injection and the amorphous layer at the bonding interface are presumably the reasons to cause SCLCs. [ABSTRACT FROM AUTHOR]