Photoresponse of the In0.3Ga0.7N metal-insulator-semiconductor photodetectors

In0.3Ga0.7N metal-insulator-semiconductor （MIS） and metal-semiconductor （MS） surface barrier photodetectors have been fabricated. The In0.3Ga0.7N epilayers were grown on sapphire by metalorganic chemical vapour deposition （MOCVD）. The photoresponse and reverse current-voltage characteristics of the In0.3Ga0.7N MIS and MS photodetectors were measured. A best zero bias responsivity of 0.18 A/W at 450 nm is obtained for the In0.3Ga0.7N MIS photodetector with 10 nm Si3N4 insulator layer, which is more than ten times higher than the In0.3Ga0.7N MS photodetector. The reason is attributed to the decrease of the interface states and increase of surface barrier height by the inserted insulator. The influence of the thickness of the Si3N4 insulator layer on the photoresponsivity of the MIS photodetector is also discussed.     

Influence of Polarization Effects on the Energy Band of AlGaN／GaN／AlGaN Heterostructures

The unintentionally doped samples of Al0.22Ga0.78N/GaN/Al0.22Ga0.78N/GaN multi-heterostructures have been designed and fabricated. The polarization induced charge and free-carrier charge distributions have been demonstrated and the energy band profile has also been calculated. The results indicate the existence of two-dimensional     

Investigation into the Energy Band Diagram and Charge Distribution in A1GaN／GaN Double Heterostructures by Self-Consistent Poisson-Schroedinger Calculations

The energy band diagram and charge distribution of the unintentional doped AIGaN/GaN/AIGaN/GaN double heterostructure were obtained by self-consistent Poisson Schroedinger calculations. The severe band tilting and high two-dimensional electron gas (2DEG) density mainly attribute to the large internal polarization intensity,which is c/ose to a linear function orAl composition. The influence orAl composition is investigated. The results show that band tilting enlarges and 2DEG gains with AI composition, and two-dimensional hole gas occurs when AI composition reaches a certain extent. The influence orAl composition and two-dimensional hole gas (2DHG)on devices is discussed.     

High-Reflectivity A1GaN/A1N Distributed Bragg Reflector in Ultraviolet Region

Thirty-pair Alo.3 Gao.T N/A1N distributed Bragg reflectors centred at 32Ohm are designed and grown on sapphire substrates by metalorganic chemical vapour deposition. No cracks are observed in the main area of the 2-inch wafer except for about 4 mm margin under an optical microscope. Regular stack of alternating layers is shown by scanning electron microscopy. Clear two-dimensional growth steps and very low surface roughness are shown by atomic force microscopy （AFM）. Well-defined periodicity is shown by high resolution x-ray diffraction. High refiectivity of 93% at 313nm with a bandwidth of 13nm is obtained.     

紫外波段SiO2/Si3N4介质膜分布式布拉格反射镜的制备与研究

采用光学传递矩阵方法设计了紫外波段SiO₂/Si₃N₄介质膜分布式布拉格反射镜, 并利用等离子体增强化学气相沉积技术在蓝宝石(0001)衬底上制备了SiO₂/Si₃N₄介质膜分布式布拉格反射镜. 光反射测试表明, 样品反射谱的峰值波长仅与理论模拟谱线相差10 nm, 并随着反射镜周期数的增加而蓝移. 由于SiO₂与Si₃N₄具有相对较大的折射率比, 因而制备的周期数为13的样品反射谱的峰值反射率就已大于99%. 样品反射谱的中心波长为333 nm, 谱峰的半高宽为58 nm. 样品截面的扫描电子显微镜和表面的原子力显微镜测量结果表明, 样品反射谱的中心波长蓝移是由子层的层厚和界面粗糙度的变化引起的. X射线反射谱表明,子层界面过渡层对于反射率的影响较小, 并且SiO₂膜的质量比Si₃N₄差, 也是造成反射率低于理论值的原因之一.