InAlN/GaN/BGaN HEMT的高温直流特性研究

对比分析了晶格匹配的InAlN/GaN与InAlN/GaN/BGaN高电子迁移率晶体管(HEMT)在不同温度(300~500 K)条件下的直流特性。结果表明,随着温度的升高,传统的InAlN/GaN HEMT器件表现出了严重的短沟道效应,具体表现在器件关断困难、栅控能力变差、阈值电压漂移以及亚阈值摆幅明显变大等。同时,由于电子限域性较差,传统的InAlN/GaN HEMT器件关态漏电现象严重。引入B摩尔分数为1.5%的BGaN缓冲层有利于InAlN/GaN HEMT器件在高温条件下仍保持较好的直流性能。当温度达到500 K时,InAlN/GaN/BGaN HEMT器件的阈值电压始终保持在-3.2 V左右,亚阈值摆幅为366 mV/dec,关态漏电流为3μA/mm,关断耗散功率为45μW/mm,均明显优于传统的InAlN/GaN HEMT器件。此外,相对于传统的InAlN/GaN HEMT而言,InAlN/GaN/BGaN HEMT器件的峰值跨导与饱和漏电流略低,但随着温度的升高,两器件的差距逐渐缩小。

Improved RF power performance of InAlN/GaN HEMT by optimizing rapid thermal annealing process for high-performance low-voltage terminal applications

Improved radio-frequency(RF)power performance of InAlN/GaN high electron mobility transistor(HEMT)is achieved by optimizing the rapid thermal annealing(RTA)process for high-performance low-voltage terminal applications.By optimizing the RTA temperature and time,the optimal annealing condition is found to enable low parasitic resistance and thus a high-performance device.Besides,compared with the non-optimized RTA HEMT,the optimized one demonstrates smoother ohmic metal surface morphology and better heterojunction quality including the less degraded heterojunction sheet resistance and clearer heterojunction interfaces as well as negligible material out-diffusion from the barrier to the channel and buffer.Benefiting from the lowered parasitic resistance,improved maximum output current density of 2279 mA·mm^(-1)and higher peak extrinsic transconductance of 526 mS·mm^(-1)are obtained for the optimized RTA HEMT.In addition,due to the superior heterojunction quality,the optimized HEMT shows reduced off-state leakage current of 7×10^(-3)mA·mm^(-1)and suppressed current collapse of only 4%,compared with those of 1×10^(-1)mA·mm^(-1)and 15%for the non-optimized one.At 8 GHz and V_(DS)of 6 V,a significantly improved power-added efficiency of 62%and output power density of 0.71 W·mm^(-1)are achieved for the optimized HEMT,as the result of the improvement in output current,knee voltage,off-state leakage current,and current collapse,which reveals the tremendous advantage of the optimized RTA HEMT in high-performance low-voltage terminal applications.

Low-resistance ohmic contacts on InAlN/GaN heterostructures with MOCVD-regrown n+-InGaN and mask-free regrowth process

This paper studied the low-resistance ohmic contacts on InAlN/GaN with metal–organic chemical vapor deposition(MOCVD)regrowth technique.The 150-nm regrown n-InGaN exhibits a low sheet resistance of 31Ω/□,resulting in an extremely low contact resistance of 0.102Ω·mm between n^(+)-InGaN and InAlN/GaN channels.Mask-free regrowth process was also used to significantly improve the sheet resistance of InAlN/GaN with MOCVD regrown ohmic contacts.Then,the diffusion mechanism between n^(+)-InGaN and InAlN during regrowth process was investigated with electrical and structural characterizations,which could benefit the further process optimization.

基于60nmT型栅f_T&f_(max)为170&210 GHz的InAlN/GaN HFETs器件（英文）

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(f_T)和最大振荡频率(f_(max))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600nm.此外,采用自对准栅工艺制备60nmT型栅.由于器件尺寸的缩小,在Vgs=1V时,器件最大饱和电流(Ids)达到1.89A/mm,峰值跨导达到462mS/mm.根据小信号测试结果,外推得到器件的f_T和f_(max)分别为170GHz和210GHz,该频率特性为国内InAlN/GaNHFETs器件频率的最高值.

InAlN/AlN/GaN HEMT器件特性研究

通过利用MOCVD生长的高质量蓝宝石衬底InAlN/AlN/GaN异质结材料,获得了高的二维电子气面密度,其值为1.65×1013cm-2。通过该结构制备了0.15μm栅长InAlN/AlN/GaN HEMT器件,获得了相关的电学特性:最大电流密度为1.3 A/mm,峰值跨导为260 mS/mm,电流增益截止频率为65 GHz,最大振荡频率为85 GHz。对比于相应的AlGaN/AlN/GaN HEMT器件,InAlN/AlN/GaN HEMT器件由于具有高的二维电子气面密度和薄的势垒层厚度,其最大电流密度和峰值跨导特性有了很大的改善,同时频率特性也有显著提高。

超薄势垒InAlN/GaN HFET器件高频特性分析

采用二次外延重掺杂n^+GaN实现非合金欧姆接触,并通过优化干法刻蚀和金属有机化学气相沉积(MOCVD)外延工艺,有效降低了欧姆接触电阻。将非合金欧姆接触工艺应用于InAlN/GaN异质结场效应晶体管(HFET)器件制备,器件的有效源漏间距缩小至600 nm。同时,结合40 nm T型栅工艺,制备了高电流截止频率(f_T)和最大振荡频率(f_(max))的InAlN/GaN HFET器件。结果显示减小欧姆接触电阻和栅长后,器件的电学特性,尤其是射频特性得到大幅提升。栅偏压为0 V时,器件最大漏源饱和电流密度达到1.88 A/mm;直流峰值跨导达到681 m S/mm。根据射频小信号测试结果外推得到器件的f_T和f_(max)同为217 GHz。

Si基超薄势垒InAlN/GaN HEMT开关器件小信号模型

为了更好地表征Si基超薄InAlN/GaN HEMT开关器件的特性和开发更精确的开关电路模型,基于0.25μm HEMT工艺制备了不同栅极电阻的开关器件,提出了附加10 kΩ栅极电阻的器件结构,并对开关器件进行了小信号模型分析。采用传统的去嵌结构提取了开关器件的寄生电容、电感和电阻参数来得到相应的本征参数。采用误差因子评估模型的准确度,结果表明模型拟合和实测的S参数基本吻合。最后将模型应用在Ku波段单刀双掷(SPDT)开关电路的设计中,实测的开启状态下该电路的插入损耗小于2.28 dB,输入回波损耗大于10 dB,输出回波损耗大于12 dB;关断状态下其隔离度大于36.54 dB。所提出的Si基InAlN/GaN HEMT模型可以为Si基HEMT的电路设计和集成提供一定的理论指导。

电流增益截止频率为236 GHz的InAlN/GaN高频HEMT

研制了高电流增益截止频率(f_T)的In Al N/Ga N高电子迁移率晶体管(HEMT)。采用金属有机化学气相沉积(MOCVD)再生长n^+GaN非合金欧姆接触工艺将器件源漏间距缩小至600 nm,降低了源、漏寄生电阻,有利于改善器件的寄生效应;使用低压化学气相沉积(LPCVD)生长SiN作为栅下介质,降低了InAlN/GaN HEMT栅漏电;利用电子束光刻实现了栅长为50 nm的T型栅。此外,还讨论了寄生效应对器件f_T的影响。测试结果表明,器件的栅漏电为3.8μA/mm,饱和电流密度为2.5 A/mm,f_T达到236 GHz。延时分析表明,器件的寄生延时为0.13 ps,在总延时中所占的比例为19%,优于合金欧姆接触工艺的结果。

Ka波段InAlN/GaN/AlGaN双异质结场效应晶体管

InAlN/GaN/AlGaN双异质结材料可以兼顾较高的二维电子气浓度和较好的载流子限域性,适宜制备Ka波段及以上微波功率器件。使用金属有机物气相外延方法,在SiC衬底上生长高性能InAlN/GaN/AlGaN双异质结构材料并制备了栅长为0.2μm的异质结场效应晶体管。测试结果表明,在栅压+2 V时器件的最大电流密度为1.12 A/mm,直流偏置条件VDS为+15 V和VGS为-1.6 V时,最高输出功率密度为2.1 W/mm,29 GHz下实现功率附加效率(ηPAE)为22.3%,截止频率fT达到60 GHz,最高振荡频率fmax为105 GHz。就功率密度和功率附加效率而言,是目前报道的Ka波段InAlN/GaN/AlGaN双异质结场效应晶体管研究的较好结果。

背势垒对InAlN/GaN异质结构中二维电子气的影响

利用有效质量理论自洽求解Poisson和Schrdinger方程理论研究了背势垒插入层对InAlN/GaN晶格匹配异质结构的电学性能的影响。研究表明,对于In0.17Al0.83N/AlN/GaN的异质结构,AlN的临界厚度为2.43 nm。此时,异质结中二维电子气(2DEG)浓度达到2.49×1013 cm-2,且不随势垒层厚度的变化而变化。重点模拟研究了具有背势垒的InAlN/AlN/GaN/AlGaN/GaN和InAlN/AlN/GaN/InGaN/GaN两种结构的能带结构和2DEG的分布情况。理论结果表明,采用AlGaN背势垒结构时,对于AlGaN的任意Al组分,GaN沟道层导带底能量均被抬升,增强了AlN/GaN三角势阱对2DEG的限制作用,提高了电子迁移率。采用InGaN/GaN作为背势垒结构,当InGaN厚度为2或3 nm时,三角势阱中的2DEG随InGaN中In组分的增加先升高后降低,这主要是由于GaN/InGaN界面处产生的正极化电荷的影响,引起电子在AlN/GaN三角势阱和InGaN/GaN势阱之间的分布变化。

结构参数对N极性面GaN/InAlN高电子迁移率晶体管性能的影响

基于漂移-扩散传输模型、费米狄拉克统计模型以及Shockley-Read-Hall复合模型等,通过自洽求解薛定谔方程、泊松方程以及载流子连续性方程,模拟研究了材料结构参数对N极性面GaN/InAlN高电子迁移率晶体管性能的影响及其物理机制.结果表明,增加GaN沟道层的厚度(5-15 nm)与InAlN背势垒层的厚度(10-40 nm),均使得器件的饱和输出电流增大,阈值电压发生负向漂移.器件的跨导峰值随Ga N沟道层厚度的增加与InAlN背势垒层厚度的减小而减小.模拟中,各种性能参数的变化趋势均随GaN沟道层与InAlN背势垒层厚度的增加而逐渐变缓,当GaN沟道层厚度超过15 nm、InAlN背势垒层厚度超过40 nm后,器件的饱和输出电流、阈值电压等参数基本趋于稳定.材料结构参数对器件性能影响的主要原因可归于器件内部极化效应、能带结构以及沟道中二维电子气的变化.

InAlN/AlN/GaN HEMT电学特性仿真与分析

研究了一种新型GaN基HEMT结构,即InAlN/AlN/GaN异质结层结构,并对其直流特性以及频率特性进行了仿真。通过理论分析,结合TCAD软件,与常规AlGaN/AlN/GaNHEMT进行对比。对栅长为1μm的器件进行仿真,结果表明,器件的最大跨导为450mS/mm,最大电流密度为2A/mm,电流增益截止频率fT=15GHz,最高振荡频率fmax=35GHz。

AlGaN插入层对InAlN/AlGaN/GaN异质结散射机制的影响

InAlN/AlN/GaN异质结中,名义上的AlN插入层实为Ga含量很高的AlGaN层, Al, Ga摩尔百分比决定了电子波函数与隧穿几率,因此影响与InAlN/AlGaN势垒层有关的散射机制.本文通过求解薛定谔-泊松方程与输运方程,研究了AlGaN层Al摩尔百分含量对InAlN组分不均匀导致的子带能级波动散射、导带波动散射以及合金无序散射三种散射机制的影响.结果显示:当Al含量由0增大到1,子带能级波动散射强度与合金无序散射强度先增大后减小,导带波动散射强度单调减小;在Al含量为0.1附近的小组分范围内,合金无序散射是限制迁移率的主要散射机制,该组分范围之外,子带能级波动散射是限制迁移率的主要散射机制;当Al摩尔百分含量超过0.52,三种散射机制共同限制的迁移率超过无插入层结构的迁移率, AlGaN层显示出对迁移率的提升作用.

InAlN/GaN异质结二维电子气波函数的变分法研究

使用变分法推导了InAlN/GaN异质结二维电子气波函数和基态能级的解析表达式,并讨论了InAlN/GaN异质结结构参数对二维电子气电学特性的影响.在假设二维电子气来源于表面态的前提下,使用了一个包含两个变分参数的尝试波函数推导电子总能量期望值,并通过寻找能量期望极小值确定变分参数.计算结果显示,二维电子气面密度随InAlN厚度的增大而增大,且理论结果与实验结果一致.二维电子气面密度增大抬高了基态能级与费米能级,并保持二者之差增大以容纳更多电子.InAlN/GaN界面处的极化强度失配随着In组分增大而减弱,二维电子气面密度随之减小,并导致基态能级与费米能级减小.所建立的模型能够解释InAlN/GaN异质结二维电子气的部分电学行为,并为电子输运与光学跃迁的研究提供了解析表达式.

偏置应力对InAlN/GaN HEMT直流特性的影响

采用直流偏置应力法对蓝宝石衬底上的InAlN/GaN HEMT器件的电流崩塌效应进行了研究。实验结果表明,在关态和开态应力后,器件直流特性明显退化,退化程度随偏置应力电压和应力时间的累积而增大。理论分析和器件仿真结果表明,关态应力引起的性能退化主要是由栅泄漏电流填充表面态形成的虚栅造成的;而开态应力引起的退化是沟道热电子被势垒层陷阱及表面态俘获产生的。因此,只有消除表面态和势垒层陷阱或者隔绝表面态形成的虚栅才能有效抑制电流崩塌。偏置应力引起的性能退化是可逆过程,在无外界激励时,经过10d左右的静置,器件基本恢复初始性能。

f_T为350 GHz的InAlN/GaN HFET高频器件研究（英文）

采用再生长n^+GaN非合金欧姆接触工艺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),器件尺寸得到有效缩小,源漏间距减小至600 nm.通过优化干法刻蚀和n^+GaN外延工艺,欧姆接触总电阻值达到0.16Ω·mm,该值为目前金属有机化学气相沉积(MOCVD)方法制备的最低值.采用自对准电子束曝光工艺实现34 nm直栅.器件尺寸的缩小以及欧姆接触的改善,器件电学特性,尤其是射频特性得到大幅提升.器件的开态电阻(R_(on))仅为0.41Ω·mm,栅压1 V下,漏源饱和电流达到2.14 A/mm.此外,器件的电流增益截止频率(f_T)达到350 GHz,该值为目前GaN基HFET器件国内报道最高值.

Short-gate AlGaN/GaN high-electron mobility transistors with BGaN buffer

Using the semi-insulating property and small lattice constant a of wurtzite BGaN alloy, we propose a BGaN buffer with a B-content of 1% to enhance two-dimensional electron gas(2 DEG) confinement in a short-gate AlGaN/GaN highelectron mobility transistor(HEMT). Based on the two-dimensional TCAD simulation, the direct current(DC) and radio frequency(RF) characteristics of the AlGaN/GaN/B_(0.01)Ga_(0.99)N structure HEMTs are theoretically studied. Our results show that the BGaN buffer device achieves good pinch-off quality and improves RF performance compared with GaN buffer device. The BGaN buffer device can allow a good immunity to shift of threshold voltage for the aspect ratio(LG/d)down to 6, which is much lower than that the GaN buffer device with L_G/d=11 can reach. Furthermore, due to a similar manner of enhancing 2 DEG confinement, the B_(0.01)Ga_(0.99)N buffer device has similar DC and RF characteristics to those the AlGaN buffer device possesses, and its ability to control short-channel effects(SCEs) is comparable to that of an Al_(0.03)Ga_(0.97)N buffer. Therefore, this BGaN buffer with very small B-content promises to be a new method to suppress SCEs in GaN HEMTs.

Numerical simulation of UV LEDs with GaN and BGaN single quantum well

The objective of this work is to simulate a single quantum well ultraviolet light emitting diode(LED) based on AlGaN/GaN/AlGaN and AlGaN/BGaN/AlGaN, by using TCAD Silvaco simulator. The first structure has a GaN quantum well taken between two layers, of n-AlGaN and p-AlGaN. The second one has a BGaN quantum well instead of GaN. We fix the concentration of the boron in BGaN to only 1% and we vary the thickness of GaN and BGaN quantum well layer from 7 to 20 nm, for the two structures. As results, we obtain respectively for GaN-LED and BGaN-LED, a maximum current of 0.52 and 0.27 mA, a maximum power spectral density of 1.935 and 6.7 W cm^(-1) eV^(-1), a maximum spontaneous emission of 3.34 × 10^(28) and 3.43 × 10^(28) s^(-1) cm^(-3) eV^(-1), and a maximum Light output power of 0.56 and 0.89 mW.

Simulation study of InAlN/GaN high-electron mobility transistor with AlInN back barrier

In this work, we use a 3-nm-thick Al0.64In0.36N back-barrier layer in In0.17Al0.83N/GaN high-electron mobility transistor （HEMT） to enhance electron confinement. Based on two-dimensional device simulations, the influences of Al0.64In0.36N back-barrier on the direct-current （DC） and radio-frequency （RF） characteristics of InAlN/GaN HEMT are investigated, theoretically. It is shown that an effective conduction band discontinuity of approximately 0.5 eV is created by the 3-nm-thick Al0.64In0.36N back-barrier and no parasitic electron channel is formed. Comparing with the conventional InAlN/GaN HEMT, the electron confinement of the back-barrier HEMT is significantly improved, which allows a good immunity to short-channel effect （SCE） for gate length decreasing down to 60 nm （9-nm top barrier）. For a 70-nm gate length, the peak current gain cut-off frequency （fT） and power gain cut-off frequency （fmax） of the back-barrier HEMT are 172 GHz and 217 GHz, respectively, which are higher than those of the conventional HEMT with the same gate length.

High performance InAlN/GaN high electron mobility transistors for low voltage applications

A high performance InAlN/GaN high electron mobility transistor(HEMT)at low voltage operation(6-10 V drain voltage)has been fabricated.An 8 nm InAlN barrier layer is adopted to generate large 2DEG density thus to reduce sheet resistance.Highly scaled lateral dimension(1.2μm source-drain spacing)is to reduce access resistance.Both low sheet resistance of the InAlN/GaN structure and scaled lateral dimension contribute to an high extrinsic transconductance of 550 mS/mm and a large drain current of 2.3 A/mm with low on-resistance(Ron)of 0.9Ω·mm.Small signal measurement shows an fT/fmax of 131 GHz/196 GHz.Large signal measurement shows that the InAlN/GaN HEMT can yield 64.7%-52.7%(Vds=6-10 V)power added efficiency(PAE)associated with 1.6-2.4 W/mm output power density at 8 GHz.These results demonstrate that GaN-based HEMTs not only have advantages in the existing high voltage power and high frequency rf field,but also are attractive for low voltage mobile compatible rf applications.