光电耦合对InGaN/GaN量子阱光学性能的影响

围绕高性能GaN基垂直腔面发射激光器(VCSELs),设计了两种具有不同光电耦合强度的InGaN/GaN量子阱(QWs)样品,研究了它们的光学性质。样品A在腔模的两个波腹处各放置两个InGaN耦合量子阱,而样品B在腔模的一个波腹处放置5个InGaN耦合量子阱。计算表明样品A具有较大的相对光限制因子1.79,而样品B为1.47。光学测试发现样品A有着更高的内量子效率(IQE)和更高的辐射复合效率。使用两种样品制作了光泵VCSEL结构,在光激发下实现激射,其中基于样品A的VCSEL有着更低的激射阈值。结果表明有源区结构会显著影响量子阱与光场的耦合作用、外延片的内量子效率、辐射复合寿命和VCSEL激射阈值,同时也说明样品A的有源区结构更有利于制作低阈值的VCSEL器件。     

Silica-based microcavity fabricated by wet etching

Silica whispering gallery mode(WGM) microcavities were fabricated by the buffered oxide etcher and potassium hydroxide wet etching technique without any subsequent chemical or laser treatments. The silicon pedestal underneath was an octagonal pyramid, thus providing a pointed connection area with the top silica microdisk while weakly influencing the resonance modes. The sidewalls of our microdisks were wedge shaped, which was believed to be an advantage for the mode confinement. Efficient coupling from and to the 60 μm diameter microdisk structure was achieved using tapered optical fibres, exhibiting a quality factor of 1.5×10~4 near a wavelength of 1550 nm. Many resonance modes were observed, and double transverse electric modes were identified by theoretical calculations. The quality factor of the microdisks was also analysed to deduce the cavity roughness. The wet etching technique provides a more convenient avenue to fabricate WGM microdisks than conventional fabrication methods.     

Influence of barrier thickness on the structural and optical properties of InGaN/GaN multiple quantum wells

The structural and optical properties of InGaN/GaN multiple quantum wells(MQWs) with different barrier thicknesses are studied by means of high resolution X-ray diffraction(HRXRD), a cross-sectional transmission electron microscope(TEM), and temperature-dependent photoluminescence(PL) measurements. HRXRD and cross-sectional TEM measurements show that the interfaces between wells and barriers are abrupt and the entire MQW region has good periodicity for all three samples. As the barrier thickness is increased, the temperature of the turning point from blueshift to redshift of the S-shaped temperature-dependent PL peak energy increases monotonously, which indicates that the localization potentials due to In-rich clusters is deeper. From the Arrhenius plot of the normalized integrated PL intensity, it is found that there are two kinds of nonradiative recombination processes accounting for the thermal quenching of photoluminescence,and the corresponding activation energy(or the localization potential) increases with the increase of the barrier thickness.The dependence on barrier thickness is attributed to the redistribution of In-rich clusters during the growth of barrier layers,i.e., clusters with lower In contents aggregate into clusters with higher In contents.