高反射率电极及n-GaN表面粗化的InGaN/GaN多量子阱LED的研制

采用高反射率的Cr/Al/Pd/Au作为LED的p-GaN和n-GaN金属电极,替代低反射率的Cr/Pd/Au电极,减小了金属电极对光的吸收,使入射到高反射率金属电极的光经过反射后增加了出射概率,提高了光萃取效率。通过进一步粗化n-GaN表面,抑制了n-GaN/空气界面的光全反射,提高了光萃取效率。实验结果表明,在350mA电流下,采用高反射率的Cr/Al/Pd/Au电极的LED相比传统电极LED光输出增加了14.3%;结合n-GaN表面粗化,LED的光输出则增加了35.3%。

In-situ wafer bowing measurements of GaN grown on Si(111) substrate by reflectivity mapping in metal organic chemical vapor deposition system

In this work, the wafer bowing during growth can be in-situ measured by a reflectivity mapping method in the 3×2 Thomas Swan close coupled showerhead metal organic chemical vapor deposition（MOCVD） system. The reflectivity mapping method is usually used to measure the film thickness and growth rate. The wafer bowing caused by stresses（tensile and compressive） during the epitaxial growth leads to a temperature variation at different positions on the wafer, and the lower growth temperature leads to a faster growth rate and vice versa. Therefore, the wafer bowing can be measured by analyzing the discrepancy of growth rates at different positions on the wafer. Furthermore, the wafer bowings were confirmed by the ex-situ wafer bowing measurement. High-resistivity and low-resistivity Si substrates were used for epitaxial growth. In comparison with low-resistivity Si substrate, Ga N grown on high-resistivity substrate shows a larger wafer bowing caused by the highly compressive stress introduced by compositionally graded Al Ga N buffer layer. This transition of wafer bowing can be clearly in-situ measured by using the reflectivity mapping method.

Influences of stress on the properties of GaN/InGaN multiple quantum well LEDs grown on Si(111) substrates

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.

Performance improvement of Ga N-based light-emitting diodes transferred from Si(111) substrate onto electroplating Cu submount with embedded wide p-electrodes

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.