基于GaN同质衬底的高迁移率AlGaN/GaNHEMT材料

研究了表面预处理对GaN同质外延的影响,获得了高电子迁移率AlGaN/GaN异质结材料.通过NH_3/H_2混合气体与H_2交替通入反应室的方法对GaN模板和GaN半绝缘衬底进行高温预处理.研究结果表明,NH_3/H_2能够抑制GaN的分解,避免粗糙表面,但不利于去除表面的杂质,黄光带峰相对强度较高;H_2促进GaN分解,随时间延长GaN分解加剧,导致模板表面粗糙不平,AlGaN/GaN HEMT材料二维电子气迁移率降低.采用NH_3/H_2混合气体与H_2交替气氛模式处理模板或衬底表面,能够清洁表面,去除表面杂质,获得平滑的生长表面和外延材料表面,有利于提高AlGaN/GaN HEMT材料电学性能.在GaN衬底上外延AlGaN/GaN HEMT材料,2DEG迁移率达到2113 cm~2/V·s,电学性能良好.

Highmobility AlGaN/GaN high electronic mobility transistors on GaN homo-substrates

Gallium nitride (GaN) has great potential applications in high-power and high-frequency electrical devices due to its superior physical properties.High dislocation density of GaN grown on a foreign substrate leads to poor crystal quality and device reliability.The homo-epitaxial growth of GaN material has low dislocation density,which is the foundation of high performance of AlGaN/GaN highelectronic mobility transistor.However,it is difficult to prepare flat surface of GaN template or GaN substrate in thermal treatment process under the metal-organic chemical vapor deposition (MOCVD) ambient condition in which hydrogen (H₂) is commonly used to clean the substrate surface,i.e.,to remove impurities from the substrate surface,since H₂ would greatly enhance GaN decomposition in MOCVD high-temperature condition and etch GaN into roughness surface
In this work,an alternation gas model of ammonia/hydrogen (NH₃/H₂) mixed gas and H₂ gas is designed.This technique is used in a thermal treatment process of GaN template and substrate by MOCVD.Then,we in-situ grow AlGaN/GaN HEMTs (high electron mobility transistors) on GaN template and GaN substrate,respectively.A series of alternation gas samples with various H₂ treatment times is investigated.Optical microscope and atomic force microscope are used to observe the morphologies of GaN template and AlGaN/GaN HEMTs and two-dimensional electron gas (2DEG) mobility and density of AlGaN/GaN HEMTs are measured by contactless Hall measurement.Optical properties of AlGaN/GaN HEMTs are analyzed by photoluminescence at room temperature.The residual impurities of C and O in the GaN epilayer and the interfacial region between GaN epilayer and GaN substrate are analyzed by secondary ion mass spectrometry.
The study results show that H₂ enhances GaN decomposition in MOCVD at high temperature,and GaN decomposition greatly strengthens with H₂ treatment time increasing leading to rough surface and the decrease of 2DEG mobility.The NH₃/₂ mixed gas could suppress GaN decomposition and avoid roughn surface,but go against cleaning out the purity from GaN surface,and the relativive intensity of the yellow band is higher.The NH₃/₂ mixed gas and ₂ gas alternate thermal treatment model with proper ₂ treatment time on GaN template or GaN substrate,not only obtains atomically flat surface of GaN template and HEMT structure,but also cleans out the purity from GaN surface,which is conducive to the increase of the electric properties of HEMT material.The highest 2DEG mobility reaches to 2136 cm²/V·s with 1 min ₂ treatment in the alternate gas thermal treatment process grown on GaN templates and the electrical properties of HEMT material turn excellent.
Finally,an alternate model with 5 min NH₃/₂ mixed gas followed by 1 min ₂ and then 4 min mixed gas of thermal treatment process is used,the surface morphology of HEMT grown on GaN substrate shows highly uniform atomically steps and the root-mean-square value is 0.126 nm for 2 μm×2 μm scan area;the HEMT 2DEG mobility 2113 cm²/V·s grown on GaN substrate shows good electric properties,the residual impurities of C and O in the interfacial region between GaN epilayer and GaN substrates are below 1×1017 cm^-3,showing clean interfacial.