AlGaN/GaN high electron mobility transistors with InGaN back-barriers

A GaN/ultrathin InGaN/GaN heterojunction has been used to provide a back-barrier to the electrons in an AlGaN/GaN high-electron mobility transistor (HEMT). The polarization-induced electric fields in the InGaN layer raise the conduction band in the GaN buffer with respect to the GaN channel, increasing the confinement of the two-dimensional electron gas under high electric field conditions. The enhanced confinement is especially useful in deep-submicrometer devices where an important improvement in the pinchoff and 50% increase in the output resistance have been observed. These devices also showed excellent high-frequency performance, with a current gain cut-off frequency (f/sub T/) of 153 GHz and power gain cut-off frequency (f/sub max/) of 198 GHz for a gate length of 100 nm. At a different bias, a record f/sub max/ of 230 GHz was obtained.     

Selectively Doped High-Power AlGaN/InGaN/GaN MOS-DHFET

We describe a novel AlGaN/InGaN/GaN metal-oxide-semiconductor double heterostructure field-effect transistor with peak drain current of 1.67 A/mm and 2-GHz RF power of 15 W/mm at a drain bias as low as 35 V. These high values of peak currents and high RF powers at relatively low drain bias resulted from an additional selective area doping of the access regions during the device fabrication. The RF-output power of 12.5 W/mm (at a drain bias of V_D=30 V) was stable within a 0.5-dB variations during a 100-h continuous-wave stress test     

InGaN/GaN和InGaN/AlGaN多量子阱中应变对光致发光特性的影响

对蓝宝石衬底上的InGaN/GaN和InGaN/AlGaN多量子阱结构和经激光剥离去除衬底的InGaN/GaN和InGaN/AlGaN多量子阱结构薄膜样品,进行了光致发光谱、高分辨XRD和喇曼光谱测量.PL测量结果表明,相对于带有蓝宝石衬底的样品,InGaN/GaN多量子阱薄膜样品的PL谱峰值波长发生较小的蓝移,而InGaN/AlGaN多量子阱薄膜样品的PL谱峰值波长发生明显的红移;喇曼光谱的结果表明,激光剥离前后E2模的峰值从569.1减少到567.5cm-1.这说明激光剥离去除衬底使得外延层整体的压应力得到部分释放,但InGaN/GaN与InGaN/AlGaN多量子阱结构中阱层InGaN的应力发生了不同的变化.XRD的结果证实了这一结论.     

InGaN/GaN 和 InGaN/AlGaN 多量子阱中应变对光致发光特性的影响

对蓝宝石衬底上的InGaN/GaN和InGaN/AlGaN多量子阱结构和经激光剥离去除衬底的InGaN/GaN和InGaN/AlGaN多量子阱结构薄膜样品，进行了光致发光谱、高分辨XRD和喇曼光谱测量. PL测量结果表明，相对于带有蓝宝石衬底的样品，InGaN/GaN多量子阱薄膜样品的PL谱峰值波长发生较小的蓝移，而InGaN/AlGaN多量子阱薄膜样品的PL谱峰值波长发生明显的红移；喇曼光谱的结果表明，激光剥离前后E2模的峰值从569.1减少到567.5cm-1. 这说明激光剥离去除衬底使得外延层整体的压应力得到部分释放，但InGaN/GaN与InGaN/AlGaN多量子阱结构中阱层InGaN的应力发生了不同的变化. XRD的结果证实了这一结论.     

InGaN/GaN和InGaN/AlGaN多量子阱中应变对光致发光特性的影响

对蓝宝石衬底上的InGaN/GaN和InGaN/AlGaN多量子阱结构和经激光剥离去除衬底的InGaN/GaN和InGaN/AlGaN多量子阱结构薄膜样品,进行了光致发光谱、高分辨XRD和喇曼光谱测量.PL测量结果表明,相对于带有蓝宝石衬底的样品,InGaN/GaN多量子阱薄膜样品的PL谱峰值波长发生较小的蓝移,而InGaN/AlGaN多量子阱薄膜样品的PL谱峰值波长发生明显的红移;喇曼光谱的结果表明,激光剥离前后E2模的峰值从569.1减少到567.5cm-1.这说明激光剥离去除衬底使得外延层整体的压应力得到部分释放,但InGaN/GaN与InGaN/AlGaN多量子阱结构中阱层InGaN的应力发生了不同的变化.XRD的结果证实了这一结论.     

Impact ionization luminescence of InGaN/AlGaN/GaN p-n-heterostructures

The luminescence spectra of InGaN/AlGaN/GaN p-n heterostructures with reverse bias sufficient for impact ionization are investigated. The injection luminescence of light-emitting diodes with such structures was examined earlier. A strong electric field is present in the InGaN active layer of the heterostructures, and for small reverse bias the tunneling component of the current predominates. Avalanche breakdown commences at voltages V _th>8–10 V, i.e., ∼3E _g , (E _g is the width of the band gap) in the absence of lightly doped structures. The luminescence spectra have a short-wavelength edge corresponding to the width of the GaN band gap (3.40 eV) and maxima in the region 2.60–2.80 eV corresponding to the maxima of the injection luminescence spectra in the active layer. The long-wavelength edge of the spectra in the region 1.7–1.8 eV may be associated with deep recombination levels. Mechanisms of recombination of the hot electron-hole plasma in the strong electric fields of the p-n heterostructures are discussed. Fiz. Tekh. Poluprovodn. 32, 63–67 (January 1998)     

Electroreflectance spectra of InGaN/AlGaN/GaN quantum-well heterostructures

p?n InGaN/AlGaN/GaN heterostructures with InGaN/AlGaN multiple quantum wells are studied by electroreflectance spectroscopy. The structures are grown by metal—organic epitaxy and arranged with the p region in contact with the heat sink. Light is incident on and reflected from the structures through the sapphire substrate. To modulate the reflectivity, rectangular voltage pulses and a dc reverse bias are applied to the p?n junction. A line corresponding to interband transitions in the region of InGaN/AlGaN multiple quantum wells is observed in the electroreflectance spectra. The peak of this line is shifted to shorter wavelengths from the peak of injection luminescence of the light-emitting diode structures. The low-field model developed by Aspnes is used to describe the electroreflectance spectra. By choosing the parameters of the model to fit the experimental data, the effective band gap of the active region of the structure, E _g ^* , is determined at 2.76–2.78 eV. The experimental dependence of E _g ^* on the applied voltage is attributed to the effect of piezoelectric fields in the InGaN quantum wells. In the electroreflectance spectra, an interference pattern is observed in the wide spectral range from 1.4 to 3.2 eV. The interference is due to the dependence of the effective refractive index on the electric field.     

Lasing in the vertical direction in InGaN/GaN/AlGaN structures with InGaN quantum dots

InGaN/GaN structures with dense arrays of InGaN nanodomains were grown by metallorganic chemical vapor deposition. Lasing in vertical direction occurs at low temperatures, indicating ultrahigh gains (～ 10⁵ cm^?1) in the active region. Fabrication of an effective AlGaN/GaN distributed Bragg reflector with reflectivity exceeding 90% enables vertical lasing at room temperature in structures with a bottom distributed Bragg reflector, despite the absence of a well-reflecting upper mirror. The lasing wavelength is 401 nm, and the threshold excitation density is 400 kW/cm².     

DC and RF Characteristics of AlGaN/GaN/InGaN/GaN Double-Heterojunction HEMTs

We present the detailed dc and radio-frequency characteristics of an Al_0.3Ga_0.7N/GaN/In_0.1Ga_0.9 N/GaN double-heterojunction HEMT (DH-HEMT) structure. This structure incorporates a thin (3 nm) In_0.1Ga_0.9N notch layer inserted at a location that is 6-nm away from the AlGaN/GaN heterointerface. The In_0.1Ga_0.9N layer provides a unique piezoelectric polarization field which results in a higher potential barrier at the backside of the two-dimensional electron gas channel, effectively improving the carrier confinement and then reducing the buffer leakage. Both depletion-mode (D-mode) and enhancement-mode (E-mode) devices were fabricated on this new structure. Compared with the baseline AlGaN/GaN HEMTs, the DH-HEMT shows lower drain leakage current. The gate leakage current is also found to be reduced, owing to an improved surface morphology in InGaN-incorporated epitaxial structures. DC and small- and large-signal microwave characteristics, together with the linearity performances, have been investigated. The channel transit delay time analysis also revealed that there was a minor channel in the InGaN layer in which the electrons exhibited a mobility slightly lower than the GaN channel. The E-mode DH-HEMTs were also fabricated using our recently developed CF₄-based plasma treatment technique. The large-signal operation of the E-mode GaN-based HEMTs was reported for the first time. At 2 GHz, a 1times100 mum E-mode device demonstrated a maximum output power of 3.12 W/mm and a power-added efficiency of 49% with single-polarity biases (a gate bias of +0.5 V and a drain bias of 35 V). An output third-order interception point of 34.7 dBm was obtained in the E-mode HEMTs     

SiO/sub 2//AlGaN/InGaN/GaN MOSDHFETs

The characteristics of a novel nitride based field-effect transistor combining SiO/sub 2/ gate isolation and an AlGaN/InGaN/GaN double heterostructure design (MOSDHFET) are reported. The double heterostructure design with InGaN channel layer significantly improves confinement of the two-dimensional (2-D) electron gas and compensates strain modulation in AlGaN barrier resulting from the gate voltage modulations. These decrease the total trapped charge and hence the current collapse. The combination of the SiO/sub 2/ gate isolation and improved carrier confinement/strain management results in current collapse free MOSDHFET devices with gate leakage currents about four orders of magnitude lower than those of conventional Schottky gate HFETs.     

Analysis of Interface Scattering in AlGaN/GaN/InGaN/GaN Double-Heterojunction High-Electron-Mobility Transistors

This paper presents detailed investigations on the direct-current (DC) characteristics of an AlGaN/GaN/InGaN/GaN double-heterojunction high-electron-mobility transistor (DH-HEMT) using two-dimensional numerical analysis. In this work, the hot-electron effect is taken into account and implemented in the hydrodynamic model. The results indicate that carrier transport in this kind of device exhibits properties significantly different from that in a conventional AlGaN/GaN HEMT. Due to imperfections at the GaN/InGaN interface, scattering caused by the interface roughness, phonons, etc. inhibit the negative differential conductance in high electric field. In addition, the velocity increment of electrons around the gate edge is dominated by the overshoot effect rather than the phonon effect. The energy exchange between phonons and electrons, as presented in this paper, illustrates that the dissipated power is just a small portion of the exchanged energy. For further performance improvement, more lattice-matched material with strong polarization for the barrier layer is proposed.     

A GaN/InGaN/AlGaN MQW RTD for versatile MVL applications with improved logic stability

To improve the logic stability of conventional multi-valued logic (MVL) circuits designed with a GaN-based resonate tunneling diode (RTD),we proposed a GaN/InGaN/AlGaN multi-quantum well (MQW) RTD.The proposed RTD was simulated through solving the coupled Schrodinger and Poisson equations in the numerical non-equilibrium Green's function (NEGF) method on the TCAD platform.The proposed RTD was grown layer by layer in epitaxial technologies.Simulated results indicate that its current-voltage characteristic appears to have a wider total negative differential resistance region than those of conventional ones and an obvious hysteresis loop at room temperature.To increase the Al composite of AlGaN barrier layers properly results in increasing of both the total negative differential resistance region width and the hysteresis loop width,which is helpful to improve the logic stability of MVL circuits.Moreover,the complement resonate tunneling transistor pair consisted of the proposed RTDs or the proposed RTD and enhanced mode HEMT controlled RTD is capable of generating versatile MVL modes at different supply voltages less than 3.3 V,which is very attractive for implementing more complex MVL function digital integrated circuits and systems with less devices,super high speed linear or nonlinear ADC and voltage sensors with a built-in super high speed ADC function.     

Normally-Off AlGaN/GaN HEMTs with InGaN cap layer: A simulation study

AlGaN/GaN high electron mobility transistors (HEMTs) are favored for the use in high-power and high-frequency applications. Normally-off operation has been desired for various applications, but proved to be difficult to achieve. Recently, a new approach was proposed by Mizutani et al. [Mizutani T, Ito M, Kishimoto S, Nakamura F. AlGaN/GaN HEMTs with thin InGaN cap layer for normally-off operation. IEEE Elec Dev Lett 2007;28(7):549–51]: a thin InGaN cap layer introduces a polarization field, which raises the conduction band of the AlGaN/GaN interface. As a result, the threshold voltage is shifted in positive direction. Relying on the experimental work of Mizutani et al. we conduct a simulation study of the proposed devices. Our device simulation tool is expanded by material models for InN and InGaN and also an improved high-field mobility model accounting for the specifics of the III-N materials. Using this setup, we further explore the device specific effects and conduct an analysis of the AC characteristics.     

最大振荡频率为200 GHz的蓝宝石衬底AlGaN/GaN HEMT

本文报道了fmax为200GHz的基于蓝宝石衬底的AlGaN/GaN 高电子迁移率晶体管（HEMT）。外延材料结构采用了InGaN背势垒层来减小短沟道效应,器件采用了凹栅槽和T型栅结合的工艺,实现了Ka波段AlGaN/GaN HEMT。器件饱和电流达到1.1A/mm,跨导为421mS/mm,截止频率（fT）为30GHz,最大振荡频率（fmax）为105GHz。采用了湿法腐蚀工艺将器件的Si3N4钝化层去除后,器件的Cgs和Cgd减小,器件截止频率提高到50GHz,最大振荡频率提高到200GHz。     

最大振荡频率为200GHz的蓝宝石衬底AlGaN/GaN HEMT

报道了最大振荡频率为200 GHz的基于蓝宝石衬底的AlGaN/GaN高电子迁移率晶体管(HEMT).外延材料结构采用InGaN背势垒层来减小短沟道效应,器件采用凹栅槽和T型栅结合的工艺,实现了Ka波段AlGaN/GaNHEMT.器件饱和电流达到1.1 A/mm,跨导为421 mS/mm,截止频率(fT)为30 GHz...     

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.     

Improved RF modeling techniques for enhanced AlGaN/GaN HFETs

Modeling procedures of an AlGaN/GaN HFET that incorporate the effects of both a GaN cap layer and an AlN sub-buffer layer are presented. A single off-state measurement method to extract all eight parasitic elements of an enhanced HFET has been successfully applied. In addition, procedures to model the nonlinear drain-to-source current characteristics featuring a kink are described.     

Performance assessment and sub-threshold analysis of gate material engineered AlGaN/GaN HEMT for enhanced carrier transport efficiency

The present work explores the features of gate material engineered (GME) AlGaN/GaN high electron mobility transistor (HEMT) for enhanced carrier transport efficiency (CTE) and suppressed short channel effects (SCEs) using 2-D sub-threshold analysis and device simulation. The model accurately predicts the channel potential, electric field and sub-threshold current for the conventional and GME HEMT, taking into account the effect of work function difference of the two metal gates. This is verified by comparing the model results with the ATLAS simulation results. Further, simulation study has been extended to reflect the wide range of benefits exhibited by GME HEMT for its on-state and analog performance. The simulation results demonstrate that the GME HEMT exhibits much higher on current, lower conductance and higher transconductance as compared to the conventional HEMT due to improved CTE and reduced SCEs. This in turn has a direct bearing on the device figure of merits (FOMs) such as intrinsic gain, device efficiency and early voltage. Tuning of GME HEMT in terms of the relative lengths of the two metal gates, their work function difference and barrier layer thickness has further been carried out to enhance the drive current, transconductance and the device FOMs illustrating the superior performance of GME HEMT for future high-performance high-speed switching, digital and analog applications.     

Cubic InGaN/GaN multi-quantum wells and AlGaN/GaN distributed Bragg reflectors for application in resonant cavity LEDs

In this contribution, we present results on the growth and characterization of c-InGaN/GaN MQWs and c-AlGaN/GaN DBRs, which may be used as building blocks of green (510 nm) resonant cavity light emitting diodes, which have a high potential as light sources for local area networks using plastic optical fibers. First, the impact of the indium and gallium flux on the growth of cubic-InGaN by plasma assisted molecular beam epitaxy has been studied. Indium is observed to incorporate into the c-GaInN films only when the gallium flux is reduced significantly below the value needed for stoichiometric c-GaN growth. A decrease of the surface roughness of the InGaN layers and an increase of their photoluminescence intensity per unit thickness at the transition from metal-flux limited to active nitrogen-limited growth is observed. High quality c-InGaN/GaN multi-quantum wells were grown with superlattice peaks clearly resolved in high resolution X-ray diffraction and a strong room temperature photoluminescence with a full width at half maximum of 240 meV. Cubic-AlGaN/GaN distributed Bragg reflectors with a maximum reflectivity of about 50% at 515 nm and a stop bandwidth of 33 nm have been realized. Enhanced 526 nm room temperature photoluminescence has been observed from a combined structure of a c-InGaN/GaN multi-quantum well and a c-AlGaN/GaN distributed Bragg reflector.     

氮空位在纳米GaN颗粒和InGaN/AlGaN双异质结中的聚集

直流放电等离子法制备纳米GaN颗粒中的氮缺乏可导致空位形成。在电子显微观察的电子辐照条件下，这些N-空位将进一步凝聚，形成一个a=2.209nm,b=3.826nm,c=1.037nm,α＝β＝γ＝90℃ 的调制结构。随着电子辐照剂量增加，纳米颗粒中心将出现空洞，同时使该区的金属镓离子迁移到颗粒的表面。电子显微分析及分子力学理论计算表明，这种新的调制结构系空位的有序排列所致。在此基础上，进一步研究了InGaN/AlGaN的双异质结薄膜结构中直径约为50nm的空洞存在与发光失效的关系，讨论了N－空位的聚集与空形成的关系。