A back-illuminated mesa-structure InGaAs/InP charge-compensated uni-traveling-carrier （UTC） photodi- ode （PD） is fabricated, and its saturation characteristics are investigated. The responsivity of the 40-μm- diameter 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 cansed hv cnmnlete field screening at high optical iniectinn levels
A simple method is proposed to design free- form surface for Lambertian extended source. In this method, it can take advantage of the designing method for point source via substituting each incident ray with a dynamically calculated equivalent ray. For each facet on the freeform surface, the equivalent ray emits from the energy weighted average-emitting-position for the corre- sponding incident beam, and redirects into the direction which is determined by a source-to-target mapping. The results of the designing examples show that the light distributions＇ uniformities can be improved by this method, e.g., even the improvement of 59% can be achieved.
Kun WANGYanjun HANHongtao LIYi LUOZhibiao HAOLai WANGChangzheng SUNBing XIONGJian WANG
The influences of dry-etching damage on the electrical properties of an AlGaN/GaN Schottky barrier diode with ICPrecessed anode was investigated for the first time. It was found that the turn-on voltage is decreased with the increase of dry-etching power. Furthermore, the leakage currents in the reverse bias region above pinch-off voltage rise as radio frequency（RF） power increases, while below pinch-off voltage, leakage currents tend to be independent of RF power.Based on detailed current–voltage–temperature（I–V –T） measurements, the barrier height of thermionic-field emission（TFE） from GaN is lowered as RF power increases, which results in early conduction. The increase of leakage current can be explained by Frenkel–Poole（FP） emission that higher dry-etching damage in the sidewall leads to the higher tunneling current, while below pinch-off voltage, the leakage is only related to the AlGaN surface, which is independent of RF power.
The influences of stress on the properties of InGaN/GaN multiple quantum wells （MQWs） grown on silicon substrate were investigated. The different stresses were induced by growing InGaN and A1GaN insertion layers （IL） respectively before the growth of MQWs in metal-organic chemical vapor deposition （MOCVD） system. High resolution x-ray diffrac- tion （HRXRD） and photoluminescence （PL） measurements demonstrated that the InGaN IL introduced an additional ten- sile stress in n-GaN, which released the strain in MQWs. It is helpful to increase the indium incorporation in MQWs. In comparison with MQWs without the IL, the wavelength shows a red-shift. A1GaN IL introduced a compressive stress to compensate the tensile stress, which reduces the indium composition in MQWs. PL measurement shows a blue-shift of wavelength. The two kinds of ILs were adopted to InGaN/GaN MQWs LED structures. The same wavelength shifts were also observed in the electroluminescence （EL） measurements of the LEDs. Improved indium homogeneity with InGaN IL, and phase separation with A1GaN IL were observed in the light images of the LEDs.
利用模拟软件研究施主表面态特性与AlGaN/GaN异质结构中二维电子气(2dimensional electron gas,2DEG)形成之间的关系,分析施主表面态电离过程以及表面态能级位置、表面态密度的影响。结果表明:施主表面态为2DEG的电子来源;AlGaN能带分布及2DEG密度随AlGaN厚度、施主表面态能级位置、施主表面态密度的改变而改变。
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.
Group Ⅲ-nitride material system possesses some unique properties,such as large spectrum coverage from infrared to deep ultraviolet,wide energy band gap,high electron saturation velocity,high electrical breakdown field,and strong polarization effect,which enables the big family has a very wide application range from optoelectronic to power electronic area.Furthermore,the successful growth of GaN-related III-nitride material on large size silicon substrate enable the above applications easily realize the commercialization,because of the cost-effective device fabrication on the platform of Si-based integrated circuits.In this article,the progress and development of the GaN-based materials and light-emitting diodes grown on Si substrate were summarized,in which some key issues regarding to the material growth and device fabrication were reviewed.
Migration characterizations of Ga and In adatoms on the dielectric surface in selective metal organic vapor phase epitaxy （MOVPE） were investigated. In the typical MOVPE environment, the selectivity of growth is preserved for GaN, and the growth rate of GaN micro-pyramids is sensitive to the period of the patterned SiO2 mask. A surface migration induced model was adopted to figure out the effective migration length of Ga adatoms on the dielectric surface. Different from the growth of GaN, the selective area growth of InGaN on the patterned template would induce the deposition of InGaN polycrystalline particles on the patterned Si02 mask with a long period. It was demonstrated with a scanning electron microscope and energy dispersive spectroscopy that the In adatoms exhibit a shorter migration length on the dielectric surface.
Crack-free Ga N/In Ga N multiple quantum wells（MQWs） light-emitting diodes（LEDs） are transferred from Si substrate onto electroplating Cu submount with embedded wide p-electrodes. The vertical-conducting n-side-up configuration of the LED is achieved by using the through-hole structure. The widened embedded p-electrode covers almost the whole transparent conductive layer（TCL）, which could not be applied in the conventional p-side-up LEDs due to the electrodeshading effect. Therefore, the widened p-electrode improves the current spreading property and the uniformity of luminescence. The working voltage and series resistance are thereby reduced. The light output of embedded wide p-electrode LEDs on Cu is enhanced by 147% at a driving current of 350 m A, in comparison to conventional LEDs on Si.
