AlGaN/GaN HEMTs on resistive Si(111) substrate grown by gas-sourceMBE

Al_0.3Ga_0.7N/GaN high electron mobility transistor (HEMT) structures have been grown on resistive Si(111) substrate by molecular beam epitaxy (MBE) using ammonia (NH₃). The use of an AlN/GaN intermediate layer allows a resistive buffer layer to be obtained. High sheet carrier density and high electron mobility arc obtained in the channel. A device with 0.5 μm gate length has been realised exhibiting a maximum extrinsic transconductance of 160 mS/mm and drain-source current exceeding 600 mA/mm. Small-signal measurements show f_t of 17 GHz and f_max of 40 GHz     

Properties of Semipolar GaN Grown on a Si(100) Substrate

Semiconductors - Semipolar GaN layers synthesized on a nanostructured Si(100) substrate are studied. It is shown that using a Si(100) nanoprofile combined with SixNy nanostrips on top of...     

Electron transport in passivated AlGaN/GaN/Si HEMTs

AlGaN/GaN/Si high electron mobility transistors (HEMTs) grown by molecular beam epitaxy are investigated using direct-current and radio-frequency measurements. As has been found, the maximum of drain current achieves 881 mA/mm with an extrinsic current gain cutoff frequency of 37 GHz for a 0.25 µm gate length. Pulsed characteristics also showed a reduction of trapping centers that improves the quality of the epilayers.     

AlGaN/GaN HEMTs on (111) silicon substrates

AlGaN/GaN HEMTs on silicon substrates have been fabricated and their static and small-signal RF characteristics investigated. The AlGaN/GaN material structures were grown on (111) p-Si by LP-MOVPE. Devices exhibit a saturation current of 0.91 A/mm, a good pinchoff and a peak extrinsic transconductance of 122 mS/mm. A unity current gain frequency of 12.5 GHz and f_max/f_T=0.83 were obtained. The highest saturation current reported so far, static output characteristics of up to 20 V and breakdown voltage at pinchoff higher than 40 V demonstrate that the devices are capable of handling ~16 W/mm static heat dissipation     

Comparative DC Characteristic Analysis of AlGaN/GaN HEMTs Grown on Si(111) and Sapphire Substrates by MBE

A comparative assessment of AlGaN/GaN high-electron-mobility transistors (HEMTs) grown by molecular beam epitaxy on silicon and sapphire substrates has been carried out. Large-area power GaN HEMTs with identical device dimensions were fabricated on both substrates. A thicker AlN buffer layer was used for the GaN HEMT on silicon to achieve similar quality and uniformity of GaN epitaxy for rational comparison with that grown on sapphire. Direct-current analysis and physical characterization were carried out to understand the performance of the devices. Mathematical measurement of the instability of the current–voltage (I–V) characteristic at high applied drain bias was carried out to evaluate the performance of both devices. An improved two-dimensional (2D) analysis of the I–V characteristic was performed from a thermal perspective including appropriate scattering effects on the 2D electron gas mobility. The experimental and analytical studies were correlated to reveal the effects of temperature-sensitive scattering phenomena on the mobility as well as on the I–V characteristic at high drain bias in terms of lattice thermal heating. It is observed that the HEMT on Si has improved stability compared with sapphire due to its weaker scattering phenomena at high drain bias, associated with its thermal conductivity. Simulation of 2D thermal mapping was also carried out to distinguish the hot-spot regions of the devices. The comparable electrical performance of these devices illustrates the viability of AlGaN/GaN HEMTs on Si(111) to achieve low-cost stable devices with better thermal power handling for high-voltage applications.     

MOCVD growth of cubic GaN on 3C-SiC deposited on Si (100) substrates

The growth of cubic GaN on 3C-SiC/Si(100) by metal-organic chemical vapor deposition (MOCVD) under various growth temperatures, thicknesses of 3C-SiC, and V/III ratios was studied. The fractions of cubic and hexagonal phases in the films were estimated from the integrated x-ray diffraction intensities of the cubic (002) and hexagonal (1011) planes. A smooth SiC layer, a high growth temperature, and a moderate V/III ratio are three key factors for the nucleation of the cubic phase and its subsequent growth. Hexagonal GaN with its c-axis perpendicular to the substrate preferentially grows at the low temperature of 750°C. The inclusion of the cubic phase increases with increasing growth temperature. The optimum growth conditions for dominant cubic GaN formation were a growth temperature of 950°C, a 1.5 μm thick SiC layer, and a V/III ratio of 1500. With these growth conditions, a cubic GaN layer with the cubic component of 91% was obtained.     

Porous silicon as an intermediate buffer layer for GaN growth on (100) Si

We report preliminary results on the growth of GaN on (100) Si substrate using porous silicon (PS) as an intermediate buffer layer. The growth was in situ monitored by laser beam reflectivity. Analysis of the evolution of the reflectivity signal indicates a change from relatively flat surface to rough one as the growth temperature (T_g) is increased. At a temperature of about 1050°C, the growth rate is very low and the reflected signal intensity is constant. When the growth temperature is varied, no drastic change of the porosity of the intermediate layer was detected. Scanning electron microscope (SEM) observations of the GaN/SP/Si structure revealed a good surface coverage at 500°C. When T_g increases, the structure morphology changes to columnar like structure at 600°C, and well-developed little crystallites with no preferential orientation appear at 800°C. These observations agree well with the X-ray diffraction (XRD) analysis. A preferential hexagonal growth is obtained at low growth temperature, while cubic phase begin to appear at elevated temperatures.     

Reliability of 100 nm AlGaN/GaN HEMTs for mm-wave applications

The effect of gate metallization and gate shape on the reliability and RF performance of 100 nm AlGaN/GaN HEMTs on SiC substrate for mm-wave applications has been investigated under on-state DC-stress tests. By replacing the gate metallization from NiPtAu to PtAu the median time to failure at T_ch = 209 °C can be improved from 10 h to more than 1000 h. Replacing the PtAu T-gate by a spacer gate further reduces the degradation rate under on-state stress, but decreases the current-gain cut-off frequency from 75 GHz to 50 GHz. Physical failure analysis using electroluminescence and TEM cross-section revealed pit and Ni void formation at the gate foot as the main degradation mechanisms of devices with NiPtAu T-gate. High resolution EDX mapping of stressed devices indicates that the formation of pits is caused by a local aluminium oxidation process. Simulation of the stress induced changes of the input characteristics of devices with NiPtAu gate further proves the formation of pits and Ni voids.     

30-GHz Low-Noise Performance of 100-nm-Gate-Recessed n-GaN/AlGaN/GaN HEMTs

We demonstrate a 100-nm-gate-recessed n-GaN/AlGaN/GaN high-electron mobility transistor (HEMT) with low-noise properties at 30 GHz. The recessed GaN HEMT exhibits a low ohmic-contact resistance of 0.28 $Omega cdot hbox{mm}$ and a low gate leakage current of 0.9 $muhbox{A/mm}$ when biased at $V_{rm GS} = -hbox{3} hbox{V}$ and $V_{rm DS} = hbox{10} hbox{V}$. At the same bias point, a minimum noise figure of 1.6 dB at 30 GHz and an associated gain of 5 dB were achieved. To the best of our knowledge, this is the best noise performance reported at 30 GHz for gate-recessed AlGaN/GaN HEMTs.      

ScAlN缓冲层厚度对Si(100)衬底上GaN外延层的影响

采用脉冲直流磁控溅射方法在Si(100)衬底上制备了ScAlN薄膜。以溅射的ScAlN作为缓冲层,在Si(100)衬底上用金属有机化学气相沉积(MOCVD)技术外延了GaN薄膜。使用高分辨X射线衍射、原子力显微镜和拉曼光谱研究了ScAlN缓冲层的厚度对ScAlN缓冲层和GaN外延层的影响。研究结果表明,ScAlN缓冲层的厚度是影响GaN薄膜晶体质量的重要因素。随着ScAlN厚度的增加,ScAlN的(002)面X射线衍射摇摆曲线半高宽持续减小,GaN的(002)面X射线衍射摇摆曲线半高宽先减小后增大。当ScAlN缓冲层厚度为500nm时,得到的GaN晶体质量最好,其中GaN(002)面的X射线衍射摇摆曲线半高宽为0.38°,由拉曼光谱计算得到的张应力为398.38MPa。     

Piezoresistive characteristics of short-channel MOSFETs on (100)silicon

This paper demonstrates that the intrinsic piezoresistive response of the MOSFET channel is independent of length. The reported fall-off of the piezoresistive response of the transistor in short channel devices is shown to be the result of parasitic series resistance in the source of the transistor. At the same time, the experimental results demonstrate that the threshold voltage of the devices is essentially independent of stress. The results are verified for three independent processes     

钝化前表面预处理对AlGaN/GaN HEMTs性能的影响

提出一种新的钝化技术--采用盐酸和氢氟酸混合预处理溶液(HF:HCI:H2O=1:4:20)对AIGaN/GaNHEMTs进行表面预处理后冉淀积Si3N4钝化,研究了新型钝化技术对AlGaN/GaN HEMTs性能的影响并分析其机理.与用常规方法钝化的器件相比,经过表面顶处理再钝化,成功地抑制了 AIGaN/GaN HEMTs肖特基特性的恶化,有效地增强抑制电流崩塌效应的能力,将GaN基HEMTs的输出功率密度提高到5.2W/mm,并展现良好的电学可靠性.通过X射线光电子谱(XPS)检测预处理前后的AIGaN表面,观察到经过预处理后的AIGaN表面氧元素的含量大幅度下降.表面氧元素的含量下降,能有效地降低表面态密度和表面电荷陷阱密度,被认为是提高AIGaN/GaN HEMTs性能的主要原因.     

Improved Microwave Noise Performance by SiN Passivation in AlGaN/GaN HEMTs on Si

Effects of silicon nitride (SiN) surface passivation by plasma enhanced chemical vapor deposition (PECVD) on microwave noise characteristics of AlGaN/GaN HEMTs on high-resistivity silicon (HR-Si) substrate have been investigated. About 25% improvement in the minimum noise figure $(NF_{min})$ (0.52 dB, from 2.03 dB to 1.51 dB) and 10% in the associate gain $(G_{rm a})$ (1.0 dB, from 10.3 dB to 11.3 dB) were observed after passivation. The equivalent circuit parameters and noise source parameters (including channel noise coefficient $(P)$, gate noise coefficient $(R)$, and their correlation coefficient $(C)$ ) were extracted. $P$ , $R$ and $C$ all increased after passivation and the increase of C contributes to the decrease of the noise figure. It was found that the improved microwave small signal and noise performance is mainly due to the increase of the intrinsic transconductance $(g_{{rm m}0})$ and the decrease of the extrinsic source resistance $(R_{rm s})$.      

Si(100)和Si(111)衬底上的同质分子束外延

用超高真空电子束蒸发系统进行了硅的同质分子束外延.发现采用适当的表面化学处理方法,然后在超高真空中加热,可以在较低温度下(800—814℃)获得清洁和平整的有序表面.Si(100)和Si(111)的外延分别在520℃和714℃进行,外延膜的结构和电学特性良好.     

Cubic Phase GaN on Nano‐grooved Si (100) via Maskless Selective Area Epitaxy

A method of forming cubic phase (zinc blende) GaN (referred as c‐GaN) on a CMOS‐compatible on‐axis Si (100) substrate is reported. Conventional GaN materials are hexagonal phase (wurtzite) (referred as h‐GaN) and possess very high polarization fields (～MV/cm) along the common growth direction of <0001>. Such large polarization fields lead to undesired shifts (e.g., wavelength and current) in the performance of photonic and vertical transport electronic devices. The cubic phase of GaN materials is polarization‐free along the common growth direction of <001>, however, this phase is thermodynamically unstable, requiring low‐temperature deposition conditions and unconventional substrates (e.g., GaAs). Here, novel nano‐groove patterning and maskless selective area epitaxy processes are employed to integrate thermodynamically stable, stress‐free, and low‐defectivity c‐GaN on CMOS‐compatible on‐axis Si. These results suggest that epitaxial growth conditions and nano‐groove pattern parameters are critical to obtain such high quality c‐GaN. InGaN/GaN multi‐quantum‐well structures grown on c‐GaN/Si (100) show strong room temperature luminescence in the visible spectrum, promising visible emitter applications for this technology.     

Self-assembling Ge(Si)/Si(100) quantum dots

The morphological evolution of self-assembled epitaxial quantum dots on Si(100) is reviewed. This intensely investigated material system continues to provide fundamental insight guiding the growth of nanostructured electronic materials. Self-assembled quantum dots are faceted, three-dimensional islands which grow atop a planar wetting layer. Pure Ge growth at higher substrate temperatures results in narrower island size distributions but activates additional strain-relief mechanisms which will alter the optical and electronic properties of the dots. Optical and electrical characterization has shown that electrons and holes are confined to different regions of the dot. This results in a spatially indirect, type II recombination mechanism. Emerging device applications which exploit properties of these nanoscale Ge islands are discussed.     

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.     

ZnO纳米棒与Si(111)和Si(100)衬底的外延关系(英文)

运用热蒸发技术在Si(111)和Si(100)基片上制备了ZnO纳米棒。SEM表征显示,ZnO纳米棒的直径约100nm,长度均匀,大约3μm;XRD表征发现ZnO纳米棒沿[0001]晶向择优生长。通过实验结果与理论分析得出:对于Si(111)基片上的样品,大部分ZnO纳米棒沿6个对称方向生长,而且与基片之间的夹角为54.7°,ZnO与Si(111)的外延关系为[0001]ZnO‖[114]Si,[0001]ZnO‖[4]Si,[0001]ZnO‖[141]Si,[0001]ZnO‖[4]Si,[0001]ZnO‖[411]Si,或[0001]ZnO‖[4]Si。对于Si(100)基片上的样品,大部分ZnO纳米棒沿4个对称方向生长,与基片之间的夹角为70.5°,其外延关系为[0001]ZnO‖[114]Si,[0001]ZnO‖[4]Si,[0001]ZnO‖[14]Si,或[0001]ZnO‖[14]Si。通过比较分析得出Si基片可以控制ZnO纳米棒的生长方向。     

Barrier-Layer Scaling of InAlN/GaN HEMTs

We discuss the characteristics of high-electron mobility transistors with barrier thicknesses between 33 and 3 nm, which are grown on sapphire substrates by metal-organic chemical vapor deposition. The maximum drain current (at V_G = 2.0 V) decreased with decreasing barrier thickness due to the gate forward drive limitation and residual surface-depletion effect. Full pinchoff and low leakage are observed. Even with 3-nm ultrathin barrier, the heterostructure and contacts are thermally highly stable (up to 1000degC).     

GaN HEMT的温度特性及其应用

对0.25 μm双场板结构GaN HEMT器件的温度特性进行了研究.负载牵引测试结果显示,GaN HEMT增益的温度系数为-0.02 dB/°C、饱和输出功率系数为-0.004 dB/°C.大的增益温度系数结合GaN HEMT 自热效应引起的高温升对实际应用特别是功率MMIC的设计带来了挑战.按常温设计的GaN功率MM...