InGaN/GaN MQD p–n junction photodiodes

The p–n junction photodiodes with InGaN/GaN MQD have been prepared by metal-organic chemical vapor deposition (MOCVD) growth; we achieved nanoscale InGaN self-assembled QDs in the well layers of the active region. The RT PL spectrum peak position for the fabricated InGaN/GaN MQD p–n Junction PDs is located at 464.6 nm and FWHM is 24.2 nm. After finishing device process, it was fond that the turn on voltage in forward bias and the break down voltage in reverse bias are about 3 and −13.5 V, respectively. Furthermore, with 1, 2, and 3 V applied bias, the maximum responsivity of the fabricated MQD p–n junction PD was observed at 350 nm, and the minimum of spectral response was measured at 465 nm. It was also found that the responsivity was nearly a constant from 390 to 440 nm. It seems to suggest that the spectral response in the range of 390–440 nm is due to the effect of the InGaN dots-in a-well active layers.     

Modified five-layer asymmetric coupled quantum well (M-FACQW) for giant negative refractive index change

We have analyzed the electrorefractive properties of a GaAs/AlGaAs modified five-layer asymmetric coupled quantum well (M-FACQW). The theoretical analyses show that the M-FACQW is expected to exhibit a giant negative electrorefractive index change Δn in the transparent-wavelength region away from the absorption edge. The influence of fluctuations in layer thickness on the electrorefractive properties of the M-FACQW was also investigated. Although the fluctuation in layer thickness deteriorates the characteristics of Δn in the M-FACQW, the M-FACQW still maintains a very giant Δn compared with that of a conventional rectangular quantum well without thickness fluctuation. In addition, we have fabricated the M-FACQW with monolayer accuracy by solid-source molecular beam epitaxy, and measured its photoabsorption current. The experimental results are in good agreement with the calculated properties. This indicates that the M-FACQW has great potential for use in ultra-wideband and low-voltage optical modulators and switches.     

垒层温度对InGaN量子点/量子阱复合结构内量子效率的影响

使用金属有机化学气相沉积(metal organic chemical vapor deposition, MOCVD)方法生长了三个具有不同垒层温度的InGaN/GaN量子阱。由于高密度V型坑的形成,完整的量子阱结构被破坏,转变成了InGaN量子点(quantum dots, QDs)/量子阱(quantum well, QW)复合结构。通过变功率光致发光谱和变温光致发光谱,分析了在不同的垒层温度下量子限制斯塔克效应(quantum confined Stark effect, QCSE)、非辐射复合中心密度和载流子局域化效应的变化。结果表明:在较低的垒层温度下,QCSE较弱,因为在较低的温度下,V型坑的深度较深,应力释放较明显,残余应变较低;非辐射复合中心密度也随着温度的升高而逐渐增大;样品的内量子效率(internal quantum efficiency, IQE)随着垒层生长温度的升高而降低。QCSE的增强和非辐射复合中心密度的增大是垒层生长温度升高时内量子效率下降的主要因素。