Device characteristics of the GaN/InGaN-doped channel HFETs

First dc, small signal, and RF power characteristics of GaN/InGaN doped-channel heterojunction field effect transistors (HFETs) are reported. HFETs with a 1-μm gate length have demonstrated a maximum drain current of 272 mA/mm, a flat G_m around 65 mS/mm in a V _GS between -0.65 V and +2.0 V, and an on-state breakdown voltage over 50 V. Complete pinchoff was observed for a -3.5 V gate bias. Devices with a 1-μm gate length have exhibited an f_T of 8 GHz and f_max of 20 GHz. A saturated output power of 26 dBm was obtained at 1.9 GHz for a 1 μm×1 mm device     

Monolithically integrated high-power broad-band RF switch based on III-N insulated gate transistors

We report on the high-performance monolithically integrated RF switch based on metal-oxide-semiconductor III-N heterostructure field-effect transistors (MOSHFETs). The radio frequency (RF) switch microwave monolithic integrated circuit (MMIC) consists of three submicron-gate MOSHFETs connected into /spl pi/-type configuration. In the 0-10 GHz frequency range, the insertion loss is less than 1dB and the isolation is better than 20 dB. The switching powers well exceed 20 W per 1mm of the active element width. The high performance parameters of the switch are achieved due to unique properties of III-nitride MOSHFET, which combines a low channel resistance and high breakdown voltage features of AlGaN/GaN HFETs and extremely low gate leakage currents, large gate voltage swing and low gate capacitance specific to insulated gate design. The combination of these parameters makes MOSHFETs excellent candidates for high-power switching. The experimental data obtained from the RF switch are in close agreement with the results of simulations.     

SiC and GaN transistors - is there one winner for microwave power applications?

Wide bandgap semiconductors show promise for high-power microwave electronic devices. Primarily due to low breakdown voltage, it has not been possible to design and fabricate solid-state transistors that can yield radio-frequency (RF) output power on the order of hundreds to thousands of watts. This has severely limited their use in power applications. Recent improvements in the growth of wide bandgap semiconductor materials, such as SiC and the GaN-based alloys, provide the opportunity to now design and fabricate microwave transistors that demonstrate performance previously available only from microwave tubes. The most promising electronic devices for fabrication in wide bandgap semiconductors for these applications are metal-semiconductor field-effect transistors (MESFETs) fabricated from the 4H-SiC polytype and heterojunction field-effect transistors (HFETs) fabricated using the AlGaN/GaN heterojunction. These devices can provide RF output power on the order of 5-6 W/mm and 10-12 W/mm of gate periphery, respectively. 4H-SiC MESFETs should produce useful performance at least through X band and AlGaN/GaN HFETs should produce useful performance well into the millimeter-wave region, and potentially as high as 100 GHz.     

Mechanism of current collapse removal in field-plated nitride HFETs

An experimental study of the mechanism of RF current collapse removal in high-power nitride-based HFETs is presented. The results show that the conductivity of the dielectric material under the field plate plays a crucial role in the current collapse removal. Identical geometry field plated HFETs differing only in the FP dielectric conductivity show varying degree of current collapse removal. Devices with semiconducting dielectric layers exhibit perfectly linear RF power - drain bias dependence with the output powers of 20 W/mm at 55 V drain bias with essentially no current collapse. A trapped charge discharging model is presented to explain the removal of current collapse in FPd devices.     

Current Crowding in High Performance Low-Loss HFET RF Switches

We report on an integrated low-loss, high-isolation RF switch using large periphery AlGaN/GaN heterostructure field-effect transistors (HFETs) connected in a Gamma-cell configuration. The insertion loss was below 0.27 dB and isolation exceeded 28 dB in the frequency range from direct current to 2 GHz. The unit-width ON resistance of large periphery HFETs was slightly higher than that of narrower devices due to current crowding in the metal electrodes. Modeling of the observed current crowding effect predicts that an optimized design will yield less than a 0.1 dB insertion loss, which is comparable to the best RF MEMS.     

基于60 nm T型栅fT & fmax为170 & 210 GHz 的InAlN/GaN HFETs 器件

基于蓝宝石衬底InAlN/GaN异质结材料研制具有高电流增益截止频率(fT)和最大振荡频率(fmax)的InAlN/GaN异质结场效应晶体管 (HFETs)。基于再生长n GaN欧姆接触工艺实现了器件尺寸的缩小,有效源漏间距(Lsd)缩小至600 nm。此外,采用自对准栅工艺制备60 nm T型栅。由于器件尺寸的缩小,在Vgs= 1 V下,器件最大饱和电流(Ids)达到1.89 A/mm,峰值跨导达到462 mS/mm。根据小信号测试结果,外推得到器件的fT和fmax分别为170 GHz和210 GHz,该频率特性为国内InAlN/GaN HFETs器件频率的最高值。     

Spontaneous and piezoelectric polarization effects on the outputcharacteristics of AlGaN/GaN heterojunction modulation doped FETs

We report on the calculation of electrical characteristics of AlGaN/GaN heterojunction field effect transistors (HFETs). The model is based on the self-consistent solution of the Schrodinger and Poisson equations coupled to a quasi-2D model for the current flow. Both single and double heterojunction devices are analyzed for [0001] or [000-1] growth directions. The onset of a parasitic p-channel for particular growth directions and alloy concentrations is also shown     

RF measurements and characterization of heterostructurefield-effect transistors at low temperatures

The RF performance of both conventional AlGaAs-GaAs and superlattice AlAs-GaAs heterostructure field-effect transistors (HFETs) has been investigated at 120 K, and the results are compared with room-temperature values. Both the system used for low-temperature RF measurements up to 12 GHz and the procedure used to extract the equivalent circuit from measured S-parameters of the packaged FET are described. The high-frequency performance of the HFETs is strongly improved at low temperatures but is sensitive to light due to the device structure. The problems of low-temperature measurement and the results of RF investigation are discussed. Although the gate lengths of the HFETs investigated are greater than 1 μm, the method and the results of the analysis can be transferred to submicron devices without any restrictions. Therefore, submicron superlattice HFETs may exhibit high power gain at 300 K as well as at lower temperatures both in the dark and under illumination     

High performance of induced-channel heterojunction field-effect transistor (HFET)

AlGaAs/GaAs high-performance, minority-carrier, induced-channel, heterojunction field-effect transistors (HFETs) fabricated on semi-insulating GaAs using molecular beam epitaxy (MBE) are reported. A 0.6 mu m self-aligned gate HFET exhibited a room-temperature transconductance of 540 mS/mm with a cutoff frequency of 25 GHz.<>     

Unified charge control model and subthreshold current inheterostructure field-effect transistors

A unified analytical charge control model covering the entire range of gate voltages from below and above threshold is developed for heterojunction field-effect transistors (HFETs). This model is based on a new interpretation of the quantized energy levels for the two-dimensional electron gas. It reduces to a classical charge sheet model in the limit of low surface field. The model is used to interpret the experimental data for the subthreshold regime of HFETs. The results indicate wide range variation of the effective acceptor concentration after device fabrication processing in the unintentionally doped GaAs buffer layer     

基于再生长欧姆接触工艺的220 GHz InAlN/GaN 场效应晶体管

本文在蓝宝石衬底上研制了具有高电流增益截止频率(f_T)的InAlN/GaN异质结场效应晶体管 (HFETs)。基于MOCVD外延n -GaN欧姆接触工艺实现了器件尺寸的缩小,有效源漏间距(L_sd)缩小至600 nm。此外,采用自对准工艺制备了50 nm直栅。由于器件尺寸的缩小,V_gs= 1 V下器件最大饱和电流(I_ds)达到2.11 A/mm,峰值跨导达到609 mS/mm。小信号测试表明,器件f_T达到220 GHz、最大振荡频率(f_max)达到48 GHz。据我们所知,该f_T值是目前国内InAlN/GaN HFETs器件报道的最高结果。     

New aspects and mechanism of kink effect in InAlAs/InGaAs/InPinverted HFETs

The kink effect in InAlAs/InGaAs/InP composite channel heterojunction field effect transistors (HFETs) was investigated as a function of temperature and optical excitation. Drain source and gate current measurements show that above 325 K the kink effect disappears while the impact ionization process is still present. The kink at low temperatures is suppressed by illumination with photons of energy above 1 eV. These results prove that this parasitic effect is mainly related to the presence of traps in the top layers     

Low-loss high power RF switching using multifinger AlGaN/GaN MOSHFETs

We demonstrate a novel RF switch based on a multifinger AlGaN/GaN MOSHFET. Record high saturation current and breakdown voltage, extremely low gate leakage current and low gate capacitance of the III-N MOSHFETs make them excellent active elements for RF switching. Using a single element test circuit with 1-mm wide multifinger MOSHFET we achieved 0.27 dB insertion loss and more than 40 dB isolation. These parameters can be further improved by impedance matching and by using submicron gate devices. The maximum switching power extrapolated from the results for 1A/mm 100 /spl mu/m wide device exceeds 40 W for a 1-mm wide 2-A/mm MOSHFET.     

Source resistance reduction of AlGaN-GaN HFETs with novel superlattice cap layer

We have developed a novel AlGaN-GaN heterojunction field effect transistor (HFET) with an ultralow source resistance by employing the novel superlattice (SL) cap structure. The particular advantage of the SL cap, i.e., the existence of multiple layers of the polarization-induced two-dimensional electron gas (2DEG) with high mobility and high concentration at each AlGaN-GaN interface, is fully exploited for lowering the lateral resistance and the potential barrier at the interface of the SL cap and the HFET barrier layer. By designing the AlGaN-GaN thickness ratio, we have established a method to obtain the optimized SL structure and have achieved an extremely low source resistance of 0.4 /spl Omega//spl middot/mm which is lower not only than HFETs with the conventional structure but also than those with the n-GaN cap structure. The SL cap HFET fabricated on a sapphire substrate exhibited excellent dc and RF performance, i.e., maximum transconductance of over 400 mS/mm, maximum drain current of 1.2 A/mm, a cutoff frequency of 60 GHz, a maximum frequency of oscillation of 140 GHz, and a very low noise figure minimum of 0.7 dB at 12 GHz.     

Thermal analysis of AlGaN-GaN power HFETs

In this paper, we present a thermal analysis of AlGaN-GaN power heterojunction field-effect transistors (HFETs). We report the dc, small-signal, large-signal, and noise performances of AlGaN-GaN HFETs at high temperatures. The temperature coefficients measured for GaN HFETs are lower than that of GaAs pseudomorphic high electron-mobility transistors, confirming the potential of GaN for high-temperature applications. In addition, the impact of thermal effects on the device dc, small-signal, and large-signal characteristics is quantified using a set of pulsed and continuous wave measurement setups. Finally, a thermal model of a GaN field-effect transistor is implemented to determine design rules to optimize the heat flow and overcome self-heating. Arguments from a device, circuit, and packaging perspective are presented.     

Transient Thermal Analysis of GaN Heterojunction Transistors (HFETs) for High-Power Applications

Transient thermal analysis of GaN heterojunction field-effect transistors (HFETs) was carried out in this letter, with a hybrid nonlinear finite element method (FEM) employed, i.e., combining the element-by-element FEM with the preconditioned conjugated gradient technique. The maximum temperature of the HFETs, strongly depending on the input power density and the duration time of the pulsed heat source, was captured numerically. The effects of temperature-dependent thermal conductivities of the substrates on the maximum temperature were also examined and compared for different substrate materials, such as sapphire, silicon, and SiC     

Switching Characteristics of GaN HFETs in a Half Bridge Package for High Temperature Applications

AlGaN/GaN heterojunction field effect transistors (HFETs) are expected to be a good candidate for power switching application at high temperatures. We designed and fabricated a discrete HFET package and a half bridge module using the AlGaN/GaN HFETs and SiC Schottky barrier diodes (SBDs) for high temperature applications. The half bridge module exhibited good reliability after 250 C and 400 h high temperature storage. Switching characteristics of the AlGaN/GaN HFET were investigated. Qg x Ron, which shows a figure of merit of switching operation, was more than 10 times better than commercial Si MOSFETs. The switching characteristics of the HFET showed no significant degradation up to 225 C.     

射频磁控溅射法制备AZO/p-Si异质结及其性能研究

利用射频磁控溅射法,在p-Si衬底上生长了Al掺杂的ZnO(AZO)薄膜,并进而制备了AZO/p-Si异质结。X射线衍射仪、紫外-可见光分光光度计、四探针测试仪和霍尔效应测试仪测量表明,AZO薄膜具有良好的结晶质量、光学和电学特性。暗态下的I-V测试表明,AZO/p-Si异质结具有较好的整流特性,反向饱和电流为1.29×10-6A,±2V处的正向和反向电流之比为229.41,计算得出异质结的理想因子为2.28。在标准光照下AZO/p-Si异质结呈现出明显的光生伏特效应,这种异质结太阳电池具有2.51%的光电转换效率。     

Theoretical analysis of the breakdown voltage in pseudomorphicHFETs

In this paper a two-dimensional (2-D) model based on a solution to the moments of the Boltzmann transport equation is used to study breakdown in pseudomorphic Heterojunction Field Effect Transistors (HFETs). The effects of the energy conservation equation and the space charge effects of generated carriers are studied in the model. The model is then used to study breakdown in GaAs channel and In_0.53Ga _0.47As channel HFETs. The model shows that impact ionization breakdown in these structures is dominated by generation in two regions: (1) the high field region near the corner of the gate, and (2) the channel near the top heterojunction. Next, the effect of a thin pseudomorphic layer, which has a high threshold energy for impact ionization, is studied. This layer is shown to significantly improve the breakdown. voltage of the HFET if used properly. Finally the effects of doping on breakdown voltage of these HFETs are studied. This study shows that increased doping can improve the maximum estimated output power of these devices     

InGaP/GaAs heterojunction bipolar transistor and RF power amplifier reliability

Electrothermal stress on advanced InGaP/GaAs heterojunction bipolar transistors (HBTs) was carried out experimentally. It showed a long-term stress-induced base current instability and a decrease in the DC current gain. A class-AB RF power amplifier (PA) was also considered to study the stress effect on the amplifier’s RF performance. The SPICE Gummel–Poon (SGP) model parameters were extracted from the pre- and post-stress HBT data and used in Cadence SpectreRF simulation. The amplifier’s post-stress RF characteristics, such as the output power and power-added efficiency (PAE), remained almost unchanged even though the post-stress HBT’s DC current gain had dropped to 73.6% of its initial value.