变In组分沟道的MM-HEMT材料电子输运特性研究

在变缓冲层高迁移率晶体管（MM_HEMT）器件中，二维电子气的输运性质对器件性能起着决定作用.通过低温下二维电子气横向电阻的量子振荡现象，结合变温度的Hall测量，系统研究了不同In组分沟道MM_HEMT器件中子带电子迁移率和浓度随温度的变化关系.结果表明，沟道中In组分为0.65的样品，材料电学性能最好，In组分高于0.65的样品，严重的晶格失配将产生位错，引起迁移率下降，大大影响材料和器件的性能. 关键词： 变缓冲层高迁移率晶体管 Shubnikov_de Hass 振荡     

Influence of spacer layer thickness on the current-voltage characteristics of pseudomorphic AlAs/In0.53Ga0.47As/InAs resonant tunnelling diodes

This paper investigates the dependence of current voltage characteristics of AlAs/In0.53Ga0.47As/InAs resonant tunnelling diodes （RTDs） on spacer layer thickness. It finds that the peak and the valley current density J in the negative differential resistance （NDR） region depends strongly on the thickness of the spacer layer. The measured peak to valley current ratio of RTDs studied here is shown to improve while the current density through RTDs decreases with increasing spacer layer thickness below a critical value.     

Organic Light Emitting Diodes with an Organic Acceptor/Donor Interface Involved in Hole Injection

Organic light emitting diodes with an interface of organic acceptor 3-, 4-, 9-,10-perylenetetracarboxylic dianhydride （PTCDA） and donor copper phthalocyanine （CuPc） involved in hole injection are fabricated. As compared to the conventional device using a 5 nm CuPc hole injection layer, the device using an interface of 10nm PTCDA and 5 nm CuPc layers shows much lower operating voltage with an increase of about 46% in the maximum power efficiency. The enhanced device performance is attributed to the efficient hole generation at the PTCDA/CuPc interface. This study provides a new way of designing hole injection.     

Growth and Characterization of A1GaN/A1N/GaN HEMT Structures with a Compositionally Step-Graded A1GaN Barrier Layer

A new A1GaN/A1N/GaN high electron mobility transistor （HEMT） structure using a compositionally step-graded A1GaN barrier layer is grown on sapphire by metalorganic chemical vapour deposition （MOCVD）. The structure demonstrates significant enhancement of two-dimensional electron gas （2DEG） mobility and smooth surface morphology compared with the conventional HEMT structure with high A1 composition A1GaN barrier. The high 2DEG mobility of 1806 cm2/Vs at room temperature and low rms surface roughness of 0.220 nm for a scan area of 5μm×5 μm are attributed to the improvement of interracial and crystal quality by employing the stepgraded barrier to accommodate the large lattice mismatch stress. The 2DEG sheet density is independent of the measurement temperature, showing the excellent 2DEG confinement of the step-graded structure. A low average sheet resistance of 314.5Ω/square, with a good resistance uniformity of 0.68%, is also obtained across the 50 mm epilayer wafer. HEMT devices are successfully fabricated using this material structure, which exhibits a maximum extrinsic transconductance of 218 mS/ram and a maximum drain current density of 800 mA/mm.     

新型高效太阳能电池研究进展

第三代太阳能电池以超高效率、薄膜化、低成本为主要目标,目前发展起来的有多结叠层太阳能电池、中间带太阳能电池、多激子产生太阳能电池、热载流子太阳能电池和热光伏太阳能电池等.文章简要介绍了以上几种新型太阳能电池的工作原理和最新进展,并对其发展前景作了分析和预测.     

Synthesis and Characterization of ZnO Nanoflowers Grown on AlN Films by Solution Deposition

ZnO nanoflowers are synthesized on AlN films by solution method. The synthesized nanoflowers are composed of nanorods, which are pyramidal and grow from a central point, thus forming structures that are flower-shaped as a whole. The nanoflowers have two typical morphologies： plate-like and bush-like. The XRD spectrum corresponds to the side planes of the ZnO nanorods made up of the nanoflowers. The micro-Raman spectrum of the ZnO nanoflowers exhibits the E2 （high） mode and the second order multiple-phonon mode. The photoluminescence spectrum of the ZnO nanoflowers exhibits ultraviolet emission centred at 375nm and a broad green emission centred at 526 nm.     

具有高开启/关断电流比的Al2O3/AlGaN/GaN金属氧化物半导体高电子迁移率晶体管

采用原子层淀积(ALD)方法,制备了Al₂O₃为栅介质的高性能AlGaN/GaN金属氧化物半导体高电子迁移率晶体管(MOS-HEMT)。在栅压为-20 V时,MOS-HEMT的栅漏电比Schottky-gate HEMT的栅漏电低4个数量级以上。在栅压为+2 V时,Schottky-gate HEMT的栅漏电为191μA;在栅压为+20 V时,MOS-HEMT的栅漏电仅为23.6 nA,比同样尺寸的Schottky-gate HEMT的栅漏电低将近7个数量级。AlGaN/GaN MOS-HEMT的栅压摆幅达到了±20 V。在栅压V_gs=0 V时, MOS-HEMT的饱和电流密度达到了646 mA/mm,相比Schottky-gate HEMT的饱和电流密度(277 mA/mm)提高了133%。栅漏间距为10μm的AlGaN/GaN MOS-HEMT器件在栅压为+3 V时的最大饱和输出电流达到680 mA/mm,特征导通电阻为1.47 mΩ·cm²。Schottky-gate HEMT的开启与关断电流比仅为10⁵,MOS-HEMT的开启与关断电流比超过了10⁹,超出了Schottky-gate HEMT器件4个数量级,原因是栅漏电的降低提高了MOS-HEMT的开启与关断电流比。在V_gs=-14 V时,栅漏间距为10μm的AlGaN/GaN MOS-HEMT的关断击穿电压为640 V,关断泄露电流为27μA/mm。     

具有高阈值电压和大栅压摆幅的常关型槽栅AlGaN/GaN金属氧化物半导体高电子迁移率晶体管

介绍了一种具有高阈值电压和大栅压摆幅的常关型槽栅AlGaN/GaN金属氧化物半导体高电子迁移率晶体管。采用原子层淀积(ALD)方法实现Al₂O₃栅介质的沉积。槽栅常关型AlGaN/GaN MOS-HEMT的栅长(L_g)为2 μm,栅宽(W_g)为0.9 mm(0.45 mm×2),栅极和源极(L_gs)之间的距离为5 μm,栅极和漏极(L_gd)之间的距离为10 μm。在栅压为－20 V时,槽栅常关型AlGaN/GaN MOS-HEMT的栅漏电仅为0.65 nA。在栅压为+12 V时,槽栅常关型AlGaN/GaN MOS-HEMT的栅漏电为225 nA。器件的栅压摆幅为－20~+12 V。在栅压V_gs=+10 V时,槽栅常关型AlGaN/GaN MOS-HEMT电流和饱和电流密度分别达到了98 mA和108 mA/mm (W_g=0.9 mm), 特征导通电阻为4 mΩ·cm²。槽栅常关型AlGaN/GaN MOS-HEMT的阈值电压为+4.6 V,开启与关断电流比达到了5×10⁸。当V_ds=7 V时,器件的峰值跨导为42 mS/mm (W_g=0.9 mm,V_gs=+10 V)。在V_gs=0 V时,栅漏间距为10 μm的槽栅常关型AlGaN/GaN MOS-HEMT的关断击穿电压为450 V,关断泄露电流为0.025 mA/mm。     

化学气相传输法生长ZnO单晶及性质研究

利用化学气相传输法生长了ZnO单晶.在无籽晶自发成核的条件下,使用碳辅助增强质量传输方法,得到了晶粒尺寸达4mm×10mm的ZnO晶体.利用长有GaN层的蓝宝石晶片作为衬底,得到了直径为30mm、厚2mm左右的ZnO单晶体.比较了不同温度条件下晶体生长的结果并进行热力学过程和现象了分析.用光荧光谱和X射线双晶衍射研究了ZnO晶体的性质.