Identification and elimination of inductively coupled plasma-induced defects in AlxGa1 - xN/GaN heterostructures

By using temperature-dependent Hall,variable-frequency capacitance-voltage and cathodoluminescence (CL) measurements,the identification of inductively coupled plasma (ICP)-induced defect states around the Al x Ga 1-x N/GaN heterointerface and their elimination by subsequent annealing in Al x Ga 1-x N/GaN heterostructures are systematically investigated.The energy levels of interface states with activation energies in a range from 0.211 to 0.253 eV below the conduction band of GaN are observed.The interface state density after the ICP-etching process is as high as 2.75×10 12 cm 2 ·eV 1.The ICP-induced interface states could be reduced by two orders of magnitude by subsequent annealing in N 2 ambient.The CL studies indicate that the ICP-induced defects should be Ga-vacancy related.     

Thermal annealing behaviour of Al/Ni/Au multilayer on n-GaN Schottky contacts

Recently GaN-based high electron mobility transistors (HEMTs) have revealed the superior properties of a high breakdown field and high electron saturation velocity. Reduction of the gate leakage current is one of the key issues to be solved for their further improvement. This paper reports that an Al layer as thin as 3 nm was inserted between the conventional Ni/Au Schottky contact and n-GaN epilayers, and the Schottky behaviour of Al/Ni/Au contact was investigated under various annealing conditions by current-voltage (I-V ) measurements. A non-linear fitting method was used to extract the contact parameters from the I-V characteristic curves. Experimental results indicate that reduction of the gate leakage current by as much as four orders of magnitude was successfully recorded by thermal annealing. And high quality Schottky contact with a barrier height of 0.875 eV and the lowest reverse-bias leakage current, respectively, can be obtained under 12 min annealing at 450 C in N2 ambience.     

氢化作用对低能电子束辐照下GaN发光演变的影响

结合氢在GaN中的扩散特性，运用阴极荧光（CL）谱，对氢化前后低能电子束辐照下GaN带边发光强度的演变进行了研究.实验发现，氢化前GaN在低能电子束辐照下带边发光强度呈现衰减的趋势，而氢化后带边发射强度先上升后衰减，而且氢化后的衰减比氢化前弱.1 h辐照过程中，氢化后GaN带边发光强度的变化比氢化前要小很多.另外，实验中发现经过氢化处理的GaN在辐照后20 h内没有观察到带边发射强度的恢复.研究表明氢原子在GaN中可以钝化缺陷来增强发光，但这种钝化缺陷的作用必须通过克服高的扩散势垒来实现，而低能电子束可以 关键词： 阴极荧光 低能电子束 氢化 演变     

Different temperature dependence of carrier transport properties between AlxGal-xN/InyGal-yN/GaN and Alx Gal-xN/GaN heterostruct ures

The temperature dependence of carrier transport properties of Alx Gal-xN/InyGal-yN/CaN and AlzGal-xN/GaN heterostructures has been investigated. It is shown that the Hall mobility in Alo.25Gao.75N/Ino.03Gao.97N/GaN heterostructures is higher than that in Alo.25Gao.75N/GaN heterostructures at temperatures above 500 K, even the mobility in the former is much lower than that in the latter at 300 K. More importantly, the electron sheet density in Alo.25Gao.75N/Ino.03Gao.97N/GaN heterostructures decreases slightly, whereas the electron sheet density in Al0.25Gao.75N/CaN heterostructures gradually increases with increasing temperature above 500 K. It is believed that an electron depletion layer is formed due to the negative polarization charges at the Iny Can-yN/GaN heterointerface induced by the compressive strain in the InyCal-yN channel, which effectively suppresses the parallel conductivity originating from the thermal excitation in the underlying GaN layer at high temperatures.     

Epitaxial evolution on buried cracks in a strain-controlled AlN/GaN superlattice interlayer between AlGaN/GaN multiple quantum wells and a GaN template

Epitaxial evolution of buried cracks in a strain-controlled AlN/GaN superlattice interlayer(IL) grown on GaN template, resulting in crack-free AlGaN/GaN multiple quantum wells(MQW), was investigated. The processes of filling the buried cracks include crack formation in the IL, coalescence from both side walls of the crack, build-up of an MQW-layer hump above the cracks, lateral expansion and merging with the surrounding MQW, and two-dimensional step flow growth.It was confirmed that the filling content in the buried cracks is pure GaN, originating from the deposition of the GaN thin layer directly after the IL. Migration of Ga adatoms into the cracks plays a key role in the filling the buried cracks.     

Leakage current reduction by thermal oxidation in Ni/Au Schottky contacts on lattice-matched Ino.18Al0.82N/GaN heterostructures

By using temperature-dependent current-voltage, variable-frequency capacitance-voltage, and Hall measurements, the effects of the thermal oxidation on the electrical properties of Ni/Au Schottky contacts on lattice-matched Ino.18Alo.82N/GaN heterostructures are investigated. Decrease of the reverse leakage current down to six orders of magni- tude is observed after the thermal oxidation of the Ino.18Alo.82N/GaN heterostructures at 700 ℃. It is confirmed that the reverse leakage current is dominated by the Frenkel-Poole emission, and the main origin of the leakage current is the emis- sion of electrons from a trap state near the metal/semiconductor interface into a continuum of electronic states associated with the conductive dislocations in the InxAll-xN barrier. It is believed that the thermal oxidation results in the formation of a thin oxide layer on the InxAll-xN surface, which increases the electron emission barrier height.     

The leakage current mechanisms in the Schottky diode with a thin Al layer insertion between Al0.245Ga0.755N/GaN heterostructure and Ni/Au Schottky contact

This paper investigates the behaviour of the reverse-bias leakage current of the Schottky diode with a thin Al inserting layer inserted between Al0.245Ga0.755 N/GaN heterostructure and Ni/Au Schottky contact in the temperature range of 25-350°C. It compares with the Schottky diode without Aluminium inserting layer. The experimental results show that in the Schottky diode with Al layer the minimum point of I-V curve drifts to the minus voltage, and with the increase of temperature increasing, the minimum point of I-V curve returns the 0 point. The temperature dependence of gate-leakage currents in the novelty diode and the traditional diode are studied. The results show that the Al inserting layer introduces interface states between metal and Al0.245Ga0.755N. Aluminium reacted with oxygen formed Al2O3 insulator layer which suppresses the trap tunnelling current and the trend of thermionic field emission current. The reliability of the diode at the high temperature is improved by inserting a thin Al layer.     

InAlN材料表面态性质研究

运用电流-电压(I-V), 变频电容-电压(C-V)和原子力显微镜 (AFM) 技术研究In组分分别为15%, 17%和21%的Ni/Au/-InAlN肖特基二极管InAlN 样品表面态性质 (表面态密度、时间常数和相对于InAlN 导带底的能级位置). I-V和变频 C-V方法测量得到的实验结果表明, 随着In组分增加, 肖特基势垒高度逐渐降低, 表面态密度依次增加. 变频 C-V特性还表明,随着测试频率降低, C-V曲线有序地朝正电压方向移动, 该趋势随着In组分的增加而变得更加明显, 这可能归结于InAlN表面态的空穴发射. AFM表面形貌研究揭示InAlN 表面粗糙度增加可能是表面态密度增加的主要原因. 关键词： 不同In组分的InAlN材料 表面态 电流-电压特性 变频电容-电压特性     

Different temperature dependence of carrier transport properties between AlxGa1-xN/InyGa1-yN/GaN and AlxGa1-xN/GaN heterostructures

The temperature dependence of carrier transport properties of AlxGa1-xN/InyGa1-yN/GaN and AlxGa1-xN/GaN heterostructures has been investigated.It is shown that the Hall mobility in Al0.25Ga0.75N/In0.03Ga0.97N/GaN heterostructures is higher than that in Al0.25Ga0.75N/GaN heterostructures at temperatures above 500 K,even the mobility in the former is much lower than that in the latter at 300 K.More importantly,the electron sheet density in Al0.25Ga0.75N/In0.03Ga0.97N/GaN heterostructures decreases slightly,whereas the electron sheet density in Al0.25Ga0.75N/GaN heterostructures gradually increases with increasing temperature above 500 K.It is believed that an electron depletion layer is formed due to the negative polarization charges at the InyGa1-yN/GaN heterointerface induced by the compressive strain in the InyGa1-yN channel,which e-ectively suppresses the parallel conductivity originating from the thermal excitation in the underlying GaN layer at high temperatures.     

氮化物宽禁带半导体的MOCVD大失配异质外延

以氮化镓(GaN)、AlN(氮化铝)为代表的Ⅲ族氮化物宽禁带半导体是研制短波长光电子器件和高频、高功率电子器件的核心材料体系.由于缺少高质量、低成本的同质GaN和AlN衬底,氮化物半导体主要通过异质外延,特别是大失配异质外延来制备.由此导致的高缺陷密度、残余应力成为当前深紫外发光器件、功率电子器件等氮化物半导体器件发展的主要瓶颈,严重影响了材料和器件性能的提升.本文简要介绍了氮化物半导体金属有机化学气相沉积(MOCVD)大失配异质外延的发展历史,重点介绍了北京大学在蓝宝石衬底上AlN、高Al组分AlGaN的MOCVD外延生长和p型掺杂、Si衬底上GaN薄膜及其异质结构的外延生长和缺陷控制等方面的主要研究进展.最后对Ⅲ族氮化物宽禁带半导体MOCVD大失配异质外延的未来发展做了简要展望.