76.2mm Si基AlGaN/GaN HEMT

<正>南京电子器件研究所采用含有双AlGaN过渡层的材料结构在76.2 mm(3英寸)Si衬底上外延生长了厚度超过2μm的AlGaN/GaN HEMT材料(图1),材料表面光滑、无裂纹。通过外延材料结构和生长条     

AlGaN/GaN HEMTs With Thin InGaN Cap Layer for Normally Off Operation

AlGaN/GaN HEMTs with a thin InGaN cap layer have been proposed to implement the normally off HEMTs. The key idea is to employ the polarization-induced field in the InGaN cap layer, by which the conduction band is raised, which leads to the normally off operation. The fabricated HEMT with an In_0.2Ga_0.8N cap layer with a thickness of 5 nm showed normally off operation with a threshold voltage of 0.4 V and a maximum transconductance of 85 mS/mm for the device with a 1.9-mum-long gate. By etching off the In_0.2Ga_0.8N cap layer at the access region using gate electrode as an etching mask, the maximum transconductance has increased from 85 to 130 mS/mm due to a reduction of the parasitic source resistance.     

含有Al组分阶变AlGaN过渡层的Si基AlGaN/GaN HEMT

采用一个AlN缓冲层和两个Al组分阶变的AlGaN过渡层作为中间层,在76.2mm Si衬底上外延生长出1.7μm厚无裂纹AlGaN/GaN异质结材料,利用原子力显微镜、X射线衍射、Hall效应测量和CV测量等手段对材料的结构特性和电学性能进行了表征。材料表面平整光滑,晶体质量和电学性能良好,2DEG面密度为1.12×1013cm-2,迁移率为1 208cm2/(V.s)。由该材料研制的栅长为1μm的AlGaN/GaN HEMT器件,电流增益截止频率fT达到10.4GHz,这些结果表明组分阶变AlGaN过渡层技术可用于实现高性能Si基GaN HEMT。     

AlGaN/GaN Dual-Channel Lateral Field-Effect Rectifier With Punchthrough Breakdown Immunity and Low On-Resistance

We propose an AlGaN/GaN dual-channel lateral field-effect rectifier (DCL-FER) with improved balance between the reverse breakdown voltage (BV) and on-resistance. Instead of utilizing a long single enhancement-mode (E-mode) Schottky-controlled channel to enhance the punchthrough BV but inevitably sacrifice the on-resistance, the DCL-FER features a dual channel consisting of one E-mode section and one depletion-mode (D-mode) section in series. The D-mode channel provides higher carrier density that facilitates high on-current or low on-resistance while still preventing the E-mode channel from being punched through under high reverse voltage. For rectifiers with the same physical dimensions (a drift region length of 5 ?m and a Schottky-controlled channel length of 2 ?m), the DCL-FER is shown to deliver comparable BV while featuring 53% lower on-resistance.     

Remarkable Reduction of On-Resistance by Ion Implantation in GaN/AlGaN/GaN HEMTs With Low Gate Leakage Current

We demonstrate Si ion-implanted GaN/AlGaN/GaN high-electron mobility transistors with extremely low gate leakage current and low source resistance without any recess etching process. The source/drain (S/D) regions were formed using Si ion implantation into undoped GaN/AlGaN/GaN on sapphire substrate. Using ion implantation into S/D regions with an energy of 80 keV, the performances were significantly improved. On-resistance decreased from 26.2 to 4.3 Omega^ldrmm. Saturation drain current and maximum transconductance increased from 284 to 723 mA/mm and from 48 to 147 mS/mm.     

Single-Chip Boost Converter Using Monolithically Integrated AlGaN/GaN Lateral Field-Effect Rectifier and Normally Off HEMT

We demonstrate a single-chip switch-mode boost converter that features a monolithically integrated lateral field-effect rectifier (L-FER) and a normally off transistor switch. The circuit was fabricated on a standard AlGaN/GaN HEMT epitaxial wafer grown with GaN-on-Si technology. The fabricated rectifier with a drift length of 15 $mu hbox{m}$ exhibits a breakdown voltage of 470 V, a turn-on voltage of 0.58 V, and a specific on-resistance of 2.04 $hbox{m}Omega cdot hbox{cm}^{2}$. The L-FER exhibits no reverse recovery current associated with the turn-off transient because of its unipolar nature. A prototype of GaN-based boost converter that includes monolithically integrated rectifiers and transistors is demonstrated using conventional GaN-on-Si wafers for the first time to prove the feasibility of the GaN-based power IC technology.      

AlGaN/AlN/GaN high-power microwave HEMT

In this letter, a novel heterojunction AlGaN/AlN/GaN high-electron mobility transistor (HEMT) is discussed. Contrary to normal HEMTs, the insertion of the very thin AlN interfacial layer (~1 nm) maintains high mobility at high sheet charge densities by increasing the effective ΔE_C and decreasing alloy scattering. Devices based on this structure exhibited good DC and RF performance. A high peak current 1 A/mm at V_GS=2 V was obtained and an output power density of 8.4 W/mm with a power added efficiency of 28% at 8 GHz was achieved     

MOCVD生长AlGaN/GaN/Si(111)异质结材料

利用MOCVD在Si(111)衬底上生长了无裂纹的GaN外延薄膜和AlGaN/GaN异质结构。通过优化Si衬底的浸润处理时间、AlN层厚度等参数获得了无裂纹的GaN外延薄膜,研究了SiN缓冲层和插入层厚度对AlGaN/GaN异质结电学性质的影响,2DEG的迁移率和面密度分别达到1410cm2/V.s和1.16×1013cm-2。     

Hydrogen sensors based on AlGaN/AlN/GaN HEMT

Pt/AlGaN/AlN/GaN high electron mobility transistors (HEMT) were fabricated and characterized for hydrogen sensing. Pt and Ti/Al/Ni/Au metals were evaporated to form the Schottky contact and the ohmic contact, respectively. The sensors can be operated in either the field effect transistor (FET) mode or the Schottky diode mode. Current changes and time dependence of the sensors under the FET and diode modes were compared. When the sensor was operated in the FET mode, the sensor can have larger current change of 8 mA, but its sensitivity is only about 0.2. In the diode mode, the current change was very small under the reverse bias but it increased greatly and gradually saturated at 0.8 mA under the forward bias. The sensor had much higher sensitivity when operated in the diode mode than in the FET mode. The oxygen in the air could accelerate the desorption of the hydrogen and the recovery of the sensor.     

磁控溅射AlN介质MIS栅结构的AlGaN/GaN HEMT

报道了一种X波段输出功率密度达10.4W/mm的SiC衬底AlGaN/GaN MIS-HEMT。器件研制中采用了MIS结构、凹槽栅以及场板,其中MIS结构中采用了磁控溅射的AlN介质作为绝缘层。采用MIS结构后,器件击穿电压由80V提高到了180V以上,保证了器件能够实现更高的工作电压。在8GHz、55V的工作电压下,研制的1mm栅宽AlGaN/GaN MIS-HEMT输出功率达到了10.4W,此时器件的功率增益和功率附加效率分别达到了6.56dB和39.2%。     

AlGaN/GaN HEMTs With Low Leakage Current and High On/Off Current Ratio

In this letter, we propose using an oxide-filled isolation structure followed by $hbox{N}_{2}/hbox{H}_{2}$ postgate annealing to reduce the leakage current in AlGaN/GaN HEMTs. An off-state drain leakage current that is smaller than $hbox{10}^{-9} hbox{A/mm}$ (minimum $hbox{5.1} times hbox{10}^{-10} hbox{A/mm}$) can be achieved, and a gate leakage current in the range of $hbox{7.8} times hbox{10}^{-10}$ to $hbox{9.2} times hbox{10}^{-11} hbox{A/mm}$ ($V_{rm GS}$ from $-$10 to 0 V and $V_{rm DS} = hbox{10} hbox{V}$) is obtained. The substantially reduced leakage current results in an excellent on/off current ratio that is up to $hbox{1.5} times hbox{10}^{8}$. An improved flicker noise characteristic is also observed in the oxide-filled devices compared with that in the traditional mesa-isolated GaN HEMTs.      

AlGaN/AlN/GaN肖特基二极管的电学性能

利用金属有机化学气相淀积(MOCVD)方法生长的AlGaN/AlN/GaN/蓝宝石材料制备了AlGaN肖特基二极管.器件的肖特基接触和欧姆接触分别为Ti/Pt和Ti/Al/Ti/Au,均采用电子束蒸发的方法沉积.AlGaN表面欧姆接触的比接触电阻率为7.48×10-4Ω/cm2,器件的I-V测试表明该AlGaN肖特基二极管具有较好的整流特性.根据器件的正向,I-V特性计算得到器件的势垒高度和理想因子分别为0.57eV和4.83.将器件在300℃中温退火,器件的电学性能有所改善.     

AlGaN/AlN/GaN肖特基二极管的电学性能

利用金属有机化学气相淀积(MOCVD)方法生长的AlGaN/AlN/GaN/蓝宝石材料制备了AlGaN肖特基二极管.器件的肖特基接触和欧姆接触分别为Ti/Pt和Ti/Al/Ti/Au,均采用电子束蒸发的方法沉积.AlGaN表面欧姆接触的比接触电阻率为7.48×10-4Ω/cm2,器件的I-V测试表明该AlGaN肖特基二极管具有较好的整流特性.根据器件的正向,I-V特性计算得到器件的势垒高度和理想因子分别为0.57eV和4.83.将器件在300℃中温退火,器件的电学性能有所改善.     

Normally Off n-Channel GaN MOSFETs on Si Substrates Using an SAG Technique and Ion Implantation

We have demonstrated n-channel gallium nitride (GaN) MOSFETs using a selective area growth (SAG) technique and ion implantation on a silicon substrate. Both MOSFETs realized good normally off operations. The MOSFET using the SAG technique showed a large drain current of 112 mA/mm, a lower leakage current, and a high field mobility of 113 cm²/V . s, which is, to our knowledge, the best for a GaN MOSFET on a silicon substrate.     

Normally Off AlGaN/GaN Low-Density Drain HEMT (LDD-HEMT) With Enhanced Breakdown Voltage and Reduced Current Collapse

We report a low-density drain high-electron mobility transistor (LDD-HEMT) that exhibits enhanced breakdown voltage and reduced current collapse. The LDD region is created by introducing negatively charged fluorine ions in the region between the gate and drain electrodes, effectively modifying the surface field distribution on the drain side of the HEMT without using field plate electrodes. Without changing the device physical dimensions, the breakdown voltage can be improved by 50% in LDD-HEMT, and the current collapse can be reduced. No degradation of current cutoff frequency (f_t) and slight improvement in power gain cutoff frequency (f_max) are achieved in the LDD-HEMT, owing to the absence of any additional field plate electrode     

Nonpolar AlGaN/GaN Metal–Insulator–Semiconductor Heterojunction Field-Effect Transistors With a Normally Off Operation

Nonpolar AlGaN/GaN metal–insulator–semiconductor-heterojunction field-effect transistors (MIS-HFETs) with a complete normally off operation have been demonstrated for the first time. To realize the normally off operation of the MIS-HFETs, a 2-nm-thick SiN (as an insulator) and GaN-based nonpolar epitaxial layers that are free from polarization charges are employed. We have found that a thicker nonpolar AlN buffer layer achieves a GaN layer with a narrower full width at half maximum of the X-ray rocking curve and higher electron mobility. The fabricated MIS gate structure on the AlN buffer layer successfully decreases the gate leakage current and enables a more positive gate bias of up to $+$4 V, which is advantageous to achieve a higher drain current. Moreover, the n-GaN capping layer between gate and ohmic electrodes helps to reduce parasitic resistance and suppress current collapse. The fabricated $a$-plane MIS-HFET exhibits a threshold voltage of $+$ 1.3 V with a high drain current of 112 mA/mm. The presented MIS-HFETs will be desirable in next-generation radio-frequency and power switching application fields.      

A surface-potential-based model for AlGaN/AlN/GaN HEMT

A new surface-potential-based model for AlGaN/AlN/GaN high electron mobility transistor(HEMT) is proposed in this paper. Since the high polarization effects caused by AlN interlayer favorably influence the two dimensional electron gas(2DEG) and scattering mechanisms, we first add spontaneous and piezoelectric charge terms to the source equation of surface-potential, and a mobility model for AlGaN/AlN/GaN HEMT is rewritten. Compared with TCAD simulations, the DC characteristics of AlGaN/AlN/GaN HEMT are faithfully reproduced by the new model.     

具有高击穿电压的AlN背势垒AlGaN/GaN/AlN HEMT材料

采用金属有机化学气相沉积(MOCVD)技术在4英寸(1英寸=2.54 cm)蓝宝石衬底上制备了1.2μm厚的AlN背势垒的AlGaN/GaN/AlN双异质结高电子迁移率晶体管(HEMT)材料,其AlGaN势垒层表面粗糙度(RMS)、二维电子气(2DEG)迁移率以及HEMT材料的弯曲度都较为接近于常规的高阻GaN背势垒结构的HEMT材料。由于AlN晶格常数较小,具有AlN背势垒的HEMT材料受到了更大的压应力。通过对比分析两种HEMT材料所制备的器件发现,受益于AlN背势垒层更高的禁带宽度和临界电场,由AlN背势垒HEMT材料所制备的器件三端关态击穿电压为常规高阻GaN背势垒HEMT器件的1.5倍,缓冲层漏电流则较常规高阻GaN背势垒HEMT器件低2～3个数量级。     

AlN阻挡层对AlGaN/GaNHEMT器件的影响

利用低压MOCVD技术在蓝宝石衬底上生长了AlGaN/GaN异质结和AlGaN/AlN/GaN异质结二维电子气材料,采用相同器件工艺制造出了AlGaN/GaN HEMT器件和AlGaN/AlN/GaN HEMT器件.通过对两种不同器件的比较和讨论,研究了AlN阻挡层的增加对AlGaN/GaN HEMT器件性能的影响.