AlGaN photoconductive ultraviolet detectors are fabricated to study their time response characteristics. Persistent photoconductivity,a deterring factor for the detector response time,is found to be strongly related to the grain boundary density in AlGaN epilayers.By improving the crystal-nuclei coalescence process in metal organic vapor phase epitaxy,the grain-boundary density can be reduced,resulting in an-order-of-magnitude decrease in response time.
A back-illuminated mesa-structure InGaAs/InP charge-compensated uni-traveling-carrier(UTC) photodiode(PD) is fabricated,and its saturation characteristics are investigated.The responsivity of the 40-μmdiameter PD is as high as 0.83 A/W,and the direct current(DC) saturation current is up to 275 mA.The 1-dB compression point at the 3-dB cutoff frequency of 9 GHz is measured to be 100 mA,corresponding to an output radio frequency(RF) power of up to 20.1 dBm.According to the calculated electric field distributions in the depleted region under both DC and alternating current(AC) conditions,the saturation of the UTC-PD is caused by complete field screening at high optical injection levels.
Blue In0.2 Ga0.8N multiple quantum wells (MQWs) with Inx Ga1xN (x=0.01 0.04) barriers are grown by metal organic vapour phase epitaxy.The internal quantum efficiencies (IQEs) of these MQWs are studied in a way of temperature-dependent photoluminescence spectra.Furthermore,a 2-channel Arrhenius model is used to analyse the nonradiative recombination centres (NRCs).It is found that by adopting the InGaN barrier beneath the lowest well,it is possible to reduce the strain hence the NRCs in InGaN MQWs.By optimizing the thickness and the indium content of the InGaN barriers,the IQEs of InGaN/InGaN MQWs can be increased by about 2.5 times compared with conventional InGaN/GaN MQWs.On the other hand,the incorporation of indium atoms into the intermediate barriers between adjacent wells does not improve IQE obviously.In addition,the indium content of the intermediate barriers should match with that of the lowest barrier to avoid relaxation.
