AlGaN/GaN HFET中的陷阱

提出了二维表面态和表面缺陷层构成的AlGaN/GaN HFET中的陷阱模型。自洽求解薛定谔方程和泊松方程得到异质结能带和沟道阱基态、激发态及二维表面态的波函数。发现表面高密度缺陷减薄了势垒层厚度,显著增强了热电子隧穿过程。从缺陷态发射电子和热电子隧穿构成的新陷阱模型出发,解释了HFET的瞬态电流、肖特基势垒的伏安特性和产生-复合噪声。最后讨论了改进材料生长和器件工艺来抑制陷阱效应,改善器件性能的途径。     

AlGaN/GaN/AlGaN双异质结材料生长及性质研究

基于能带理论设计并利用MOCVD技术在76.2 mm蓝宝石衬底上生长了不同GaN沟道层厚度的AlGaN/GaN/AlGaN双异质结材料.室温霍尔测试结果表明:双异质结材料的二维电子气面密度随沟道层厚度增加有所升高并趋于饱和;二维电子气迁移率则随沟道厚度增加明显升高.200 nm厚GaN沟道的双异质结材料方块电阻平均值3...     

High-power AlGaN/GaN HEMTs for Ka-band applications

We report on the fabrication and high-frequency characterization of AlGaN/GaN high-electron mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). In devices with a gate length of 160 nm, a record power density of 10.5 W/mm with 34% power added efficiency (PAE) has been measured at 40 GHz in MOCVD-grown HEMTs biased at V/sub DS/=30 V. Under similar bias conditions, more than 8.6 W/mm, with 32% PAE, were obtained on the MBE-grown sample. The dependence of output power, gain, and PAE on gate and drain voltages, and frequency have also been analyzed.     

Characterization of ALD Beryllium Oxide as a Potential High-k Gate Dielectric for Low-Leakage AlGaN/GaN MOSHEMTs

The chemical and electrical characteristics of atomic layer deposited (ALD) beryllium oxide (BeO) on GaN were studied via x-ray photoelectron spectroscopy, current–voltage, and capacitance–voltage measurements and compared with those of ALD Al₂O₃ and HfO₂ on GaN. Radiofrequency (RF) and power electronics based on AlGaN/GaN high-electron-mobility transistors are maturing rapidly, but leakage current reduction and interface defect (D _it) minimization remain heavily researched. BeO has received recent attention as a high-k gate dielectric due to its large band gap (10.6 eV) and thermal stability on InGaAs and Si, but little is known about its performance on GaN. Unintentionally doped GaN was cleaned in dilute aqueous HCl immediately prior to BeO deposition (using diethylberyllium and H₂O precursors). Formation of an interfacial layer was observed in as-deposited samples, similar to the layer formed during ALD HfO₂ deposition on GaN. Postdeposition anneal (PDA) at 700°C and 900°C had little effect on the observed BeO binding state, confirming the strength of the bond, but led to increased Ga oxide formation, indicating the presence of unincorporated oxygen in the dielectric. Despite the interfacial layer, gate leakage current of 1.1 × 10^?7 A/cm² was realized, confirming the potential of ALD BeO for use in low-leakage AlGaN/GaN metal–oxide–semiconductor high-electron-mobility transistors.     

Temperature-dependent nonlinearities in GaN/AlGaN HEMTs

Temperature-dependent nonlinearities of GaN/AlGaN HEMTs are reported. The large-signal device model of the transistor is obtained by using a physics-based analysis. The model parameters are obtained as functions of bias voltages and temperature. The analysis of the device has been carried out using a time-domain technique. f_max for a 0.23 μm×100 μm Al_0.13Ga_0.87N/GaN FET is calculated as 69 GHz at 300 K, while at 500 K, f_max decreases to 30 GHz, which are in agreement with the experimental data within 7% error. f_max as obtained from calculated unilateral gain, decreases monotonically with increasing temperature. For shorter gate lengths irrespective of the operating temperature f_max is less sensitive to bias voltage scaling. For longer gate length devices, f_max becomes less sensitive to the bias voltage scaling at elevated temperatures. 1-dB compression point (P_1-dB ) at 4 GHz for a 1 μm×500 μm Al_0.15Ga_0.85N/GaN FET is 13 dBm at 300 K. At 500 K, P_1-dB decreases to 2.5 dBm for the same operating frequency. Similar results for output referred third intercept point (OIP3) are reported for different gate length devices     

AlGaN/GaN heterojunction bipolar transistor

We demonstrate the first GaN bipolar transistor. An AlGaN/GaN HBT structure was grown by MOCVD on c-plane sapphire substrate. The emitter was grown with an Al_0.1Ga_0.9N barrier to increase the emitter injection efficiency. Cl₂ RIE was used to pattern the emitter mesa, and selectively regrown base contact pads were implemented to reduce a contact barrier associated with RIE etch damage to the base surface. The current gain of the devices was measured to be as high as three with a base width of 200 nm. DC transistor characteristics were measured to 30 V V_CE in the common emitter configuration, with an offset voltage of 5 V. A gummel plot and base contact characteristics are also presented     

High-frequency noise in AlGaN/GaN HFETs

We present in this letter the benefits of GaN-based electronic devices for low-noise MMICs. A temperature-dependent two-temperature noise model for AlGaN/GaN HFETs is implemented on a wide range of bias conditions. This study enables to access the device high-frequency noise parameters, and allow a comparison of the noise performances with SiC and GaAs technologies.     

AlGaN/GaN异质结构中的极化工程

从自洽求解薛定谔方程和泊松方程出发,研究了AlGaN/GaN量子阱电子气密度随Al组份比、势垒层厚度和栅压的变化,比较了能带带阶和极化电荷对沟道阱能带和电子气特性的影响,研究了在势垒层和缓冲层中夹入AlN及InGaN薄层的作用,计算了AlGaN/GaN/AlGaN双异质结的能带,最后探讨了势垒层能带的优化设计,提出了剪裁势垒层能带来钝化表面的新方法。     

Plasma Treatment for Leakage Reduction in AlGaN/GaN and GaN Schottky Contacts

It has been found that the reverse leakage current of AlGaN/GaN Schottky contacts can be significantly reduced by a CF₄ plasma treatment prior to the Schottky metal evaporation. The data of electrical characterization suggest that the leakage reduction is related to the modification of the semiconductor surface by plasma treatment. The leakage reduction effect was also observed in GaN Schottky contacts. Capacitance-voltage characterization of the GaN Schottky contacts indicates that the Schottky barrier height was slightly increased by the plasma treatment. A two-step surface treatment procedure, consisting of a BCI₃ plasma treatment followed by a brief CF₄ plasma treatment, has been developed as an efficient approach to reduce the reverse leakage of the Schottky contacts, while avoiding side effects related to the CF₄ plasma.     

High-performance E-mode AlGaN/GaN HEMTs

Enhancement-mode AlGaN/GaN high electron-mobility transistors have been fabricated with a gate length of 160 nm. The use of gate recess combined with a fluorine-based surface treatment under the gate produced devices with a threshold voltage of +0.1 V. The combination of very high transconductance (> 400 mS/mm) and low gate leakage allows unprecedented output current levels in excess of 1.2 A/mm. The small signal performance of these enhancement-mode devices shows a record current cutoff frequency (f/sub T/) of 85 GHz and a power gain cutoff frequency (f/sub max/) of 150 GHz.     

High-power polarization-engineered GaN/AlGaN/GaN HEMTs without surface passivation

In this paper, a high-power GaN/AlGaN/GaN high electron mobility transistor (HEMT) has been demonstrated. A thick cap layer has been used to screen surface states and reduce dispersion. A deep gate recess was used to achieve the desired transconductance. A thin SiO/sub 2/ layer was deposited on the drain side of the gate recess in order to reduce gate leakage current and improve breakdown voltage. No surface passivation layer was used. A breakdown voltage of 90 V was achieved. A record output power density of 12 W/mm with an associated power-added efficiency (PAE) of 40.5% was measured at 10 GHz. These results demonstrate the potential of the technique as a controllable and repeatable solution to decrease dispersion and produce power from GaN-based HEMTs without surface passivation.     

Transport coefficients of AlGaN/GaN heterostructures

We have experimentally determined the effective mass (m*) of GaN, the classical (τ _c), and quantum (τ _q) scattering times for a two-dimensional electron gas residing at the interface of an AlGaN/GaN heterostructure, using the Shubnikovde Haas effect. The ratio of the two scattering times, τ _c/τ _q, suggests that, at low temperatures, the scattering mechanism limiting the mobility is due to remote ionized impurities located in AlGaN. This study should provide sample growers with information useful for improving the quality of the nitride heterostuctures.     

AlGaN/GaN HFET的优化设计

从自洽求解薛定谔方程和泊松方程出发研究了不同掺杂方式下异质结能带和二维电子气的行为。发现掺杂能剪裁异质结能带的弯曲度、控制电子气的二维特性和浓度。在此基础上研究了不同掺杂方式的掺杂效率。通过掺杂和势垒结构的优化设计,得出了用δ掺杂加薄AlN隔离层的结构,既提高了电子气浓度,又保持电子气的强二维特性。从电子气浓度和栅对电子气的控制力度出发,提出了HFET势垒优化设计中的电子气浓度与势垒层厚度乘积规则。依据二维表面态理论,研究了表面态随帽层掺杂结构的变化。从前述乘积规则和表面态变化出发进行了内、外沟道异质结构的优化设计。优化结构既提高了电子气浓度和跨导,降低了欧姆接触电阻,又抑制了电流崩塌。     

增强型AlGaN/GaN/AlGaN双异质结槽栅HEMT研究

为了在获得高击穿电压的同时实现增强型器件,对AlGaN/GaN/AlGaN双异质结HEMT进行了栅槽刻蚀,得到阈值电压为0.6 V的增强型HEMT。对器件特性的变化机理进行了分析,发现刻蚀引入的陷阱态使器件的击穿性能降低。采用变频电导法,定量研究了反应离子刻蚀在AlGaN/GaN/AlGaN双异质结HEMT中引入的陷阱态。研究表明,刻蚀工艺在双异质结HEMT中引入了大量的浅能级陷阱,这些陷阱的能级主要分布在0.36~0.40 eV。     

High Al-content AlGaN/GaN MODFETs for ultrahigh performance

The use of an AlGaN layer with high Al mole-fraction is proposed to increase the equivalent figures of merit of the AlGaN/GaN MODFET structure. It is shown that the room temperature mobility has little degradation with increasing Al mole-fraction up to 50%. 0.7-μm gate-length Al_0.5Ga_0.5N/GaN MODFETs by optical lithography exhibit a current density of 1 A/mm and three-terminal breakdown voltages up to 200 V. These devices on sapphire substrates without thermal management also show CW power densities of 2.84 and 2.57 W/mm at 8 and 10 GHz, respectively, representing a marked performance improvement for GaN-based FETs     

Intrinsic noise equivalent-circuit parameters for AlGaN/GaN HEMTs

Intrinsic noise sources and their correlation in gallium-nitride high electron-mobility transistors (HEMTs) are extracted and studied. Microwave noise measurements have been performed over the frequency range of 0.8-5.8 GHz. Using measured noise and scattering parameter data, the gate and drain noise sources and their correlation are determined using an equivalent-circuit representation. This model correctly predicts the frequency-dependent noise for two devices having different gate length. Three noise mechanisms are identified in these devices, namely, those due to velocity fluctuation, gate leakage, and traps.     

Gate-First AlGaN/GaN HEMT Technology for High-Frequency Applications

This letter describes a gate-first AlGaN/GaN high-electron mobility transistor (HEMT) with a W/high- $k$ dielectric gate stack. In this new fabrication technology, the gate stack is deposited before the ohmic contacts, and it is optimized to stand the 870 $^{circ}hbox{C}$ ohmic contact annealing. The deposition of the W/high-$k$ dielectric protects the intrinsic transistor early in the fabrication process. Three different gate stacks were studied: $hbox{W}/ hbox{HfO}_{2}$, $hbox{W}/hbox{Al}_{2}hbox{O}_{3}$ , and $hbox{W}/hbox{HfO}_{2}/hbox{Ga}_{2}hbox{O}_{3}$ . DC characterization showed transconductances of up to 215 mS/mm, maximum drain current densities of up to 960 mA/mm, and more than five orders of magnitude lower gate leakage current than in the conventional gate-last Ni/Au/Ni gate HEMTs. Capacitance–voltage measurements and pulsed-$IV$ characterization show no hysteresis for the $hbox{W}/hbox{HfO}_{2}/ hbox{Ga}_{2}hbox{O}_{3}$ capacitors and low interface traps. These W/high- $k$ dielectric gates are an enabling technology for self-aligned AlGaN/GaN HEMTs, where the gate contact acts as a hard mask to the ohmic deposition.      

X-波段AlGaN/GaN HEMT功率MMIC

AlGaN/GaN高电子迁移率晶体管(HEMT)以其高输出功率密度、高电压工作和易于宽带匹配等优势将成为下一代高频固态微波功率器件.微波功率器件主要有内匹配功率管和功率单片微波集成电路(MMIC)两种结构形式,功率MMIC尽管其研制成本相对较高,但功率MMIC可实现宽带匹配,同时功率MMIC的体积较内匹配功率管小得多,是满足诸如X波段TlR组件应用不可或缺的结构形式.功率MMIC的结构形式主要有微带和共面波导(CPW)两种,相比于CPW结构,微带结构的MMIC芯片面积更小,特别是对于大栅宽器件,微带结构的通孔接地更有利于寄生参量的减小,有利于提高MMIC的性能,因此微带结构也是应用更为广泛的MMIC结构形式.     

非掺杂AlGaN/GaN微波功率HEMT

Ga N有较 Ga As更宽的禁带、更高的击穿场强、更高的电子饱和速度和更高的热导率 ,Al Ga N/Ga N异质结构不仅具有较 Ga As PHEMT中Al Ga As/In Ga As异质结构更大的导带偏移 ,而且在异质界面附近有很强的自发极化和压电极化 ,极化电场在电子势阱中形成高密度的二维电子气 ,这种二维电子气可以由不掺杂势垒层中的电子转移来产生。理论上 Al Ga N/Ga N HEMT单位毫米栅宽输出功率可达到几十瓦 ,而且其宽禁带特点决定它可以承受更高的工作结温 ,作为新一代的微波功率器件 ,Al Ga N/Ga N HEMT将成为微波大功率器件发展的方向。采…     

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