Flicker noise in GaN/Al0.15Ga0.85N dopedchannel heterostructure field effect transistors

We have investigated noise characteristics of novel GaN/Al_0.15Ga_0.85N doped channel heterostructure field effect transistors designed for high-power density applications. The measurements were carried out for various gate bias voltages V_GS and with the drain voltage V_DS varying from the linear to the saturation regions of operation V_DS>5 V. Our results show that flicker, e.g., 1/f noise, is the dominant limiting noise of these devices; and the Hooge parameter is of the order of 10 ^-5-10^-4. The gate voltage dependence of 1/f noise was observed in the linear region for all examined V_GS and in the saturation region for V_GS>0. These results indicating low values of the Hooge parameter are important for microwave applications     

新型复合沟道Al0.3Ga0.7N/Al0.05Ga0.95N/GaN HEMT低相位噪声微波单片集成压控振荡器

设计并研制了一种新型复合沟道Al0.3Ga0.7N/Al0.05Ga0.95N/GaN HEMT(CC-HEMT)微波单片集成压控振荡器(VCO),且测试了电路的性能.CC-HEMT的栅长为1μm,栅宽为100μm.叉指金属-半导体-金属(MSM)变容二极管被设计用于调谐VCO频率.为提高螺旋电感的Q值,聚酰亚胺介质被插入在电感金属层与外延在蓝宝石上GaN层之间.当CC-HEMT的直流偏置为Vgs=-3V,Vds=6V,变容二极管的调谐电压从5.5V到8.5V时,VCO的频率变化从7.04GHz到7.29GHz,平均输出功率为10dBm,平均功率附加效率为10.4%.当加在变容二极管上电压为6.7V时,测得的相位噪声为-86.25dBc/Hz(在频偏100KHz时)和-108dB/Hz(在频偏1MHz时),这个结果也是整个调谐范围的平均值.据我们所知,这个相位噪声测试结果是文献报道中基于GaN HEMT单片VCO的最好结果.     

Low-operation voltage of InGaN/GaN light-emitting diodes by using aMg-doped Al0.15Ga0.85N/GaN superlattice

Low-resistivity Mg-doped Al_0.15Ga_0.85N/GaN strained-layer superlattices were grown. In these superlattices, the maximum hole concentration is 3×10¹⁸/cm³ at room temperature. Hall-effect measurements indicate high conductivity of this structure in which the high activation efficiency is attributed to the strain-induced piezoelectric fields. This work also fabricated InGaN/GaN blue LEDs that consist of a Mg-doped Al_0.15Ga_0.85N/GaN SLs. Experimental results indicate that the LEDs can achieve a lower operation voltage of around 3 V, i.e., smaller than conventional devices which have an operation voltage of about 3.8 V     

An 8 GHz high power AlGaN/GaN HEMT VCO

A high power X-band hybrid microwave integrated voltage controlled oscillator(VCO) based on Al-GaN /GaN HEMT is presented.The oscillator design utilizes a common-gate negative resistance structure with open and short-circuit stub microstrip lines as the main resonator for a high Q factor.The VCO operating at 20 V drain bias and-1.9 V gate bias exhibits an output power of 28 dBm at the center frequency of 8.15 GHz with an efficiency of 21%.Phase noise is estimated to be -85 dBc/Hz at 100 kHz offset and -1...     

一个8GHz高功率AlGaN/GaN HEMT VCO

基于中科院微电子所的AlGaN/GaN HEMT工艺研制了一个X波段高功率混合集成压控振荡器（VCO）。电路采用源端调谐的负阻型结构,主谐振腔由开路微带和短路微带并联构成,实现高Q值设计。在偏置条件为VD=20V, VG=-1.9V, ID=150mA时,VCO在中心频率8.15 GHz处输出功率达到28 dBm,效率21%,相位噪声-85 dBc/Hz@100 KHz,-128 dBc/Hz@1 MHz。调谐电压0~5V时,调谐范围50 MHz。分析了器件闪烁噪声对GaN HEMT基振荡器相位噪声性能的主导作用。测试结果显示了AlGaN/GaN HEMT工艺在高功率低噪声微波频率源中的应用前景。     

The influence of 1 nm AlN interlayer on properties of the Al0.3Ga0.7N/AlN/GaN HEMT structure

The sheet carrier concentrations, conduction band profiles and amount of free carriers in the barriers have been determined by solving coupled Schrödinger and Poisson equation self-consistently for coherently grown Al_0.3Ga_0.7N/GaN and Al_0.3Ga_0.7N/AlN/GaN structures on thick GaN. The Al_0.3Ga_0.7N/GaN heterojunction structures with and without 1 nm AlN interlayer have been grown by MOCVD on sapphire substrate, the physical properties for these two structures have been investigated by various instruments such as Hall measurement and X-ray diffraction. By comparison of the theoretical and experimental results, we demonstrate that the sheet carrier concentration and the electrons mobility would be improved by the introduction of an AlN interlayer for Al_0.3Ga_0.7N/GaN structure. Mechanisms for the increasing of the sheet carrier concentration and the electrons mobility will be discussed in this paper.     

Gate length scaling for Al0.2Ga0.8N/GaNHJFETs: two-dimensional full band Monte Carlo simulation includingpolarization effect

Two-dimensional self-consistent full band Monte Carlo (FBMC) simulator was developed for electron transport in wurtzite phase AlGaN/GaN heterojunction (HJ) FET. Recessed gate Al_0.2Ga_0.8N/GaN HJFET structures with an undoped cap layer were simulated, where the spontaneous and piezoelectric polarization effects were taken into account. The polarization effect was shown to not only increase the current density, but also improve the carrier confinement, and hence improve the transconductance. An off-state drain breakdown voltage (BV_ds) of 300 V and a maximum linear output power (P_max) of 46 W/mm were predicted for a 0.9-μm gate device. For a 0.1-μm gate device, 60 V BV_ds , 20 W/mm P_max, and 160 GHz current-gain cutoff frequency were predicted. Although there is considerable uncertainty due to lack of information on the band structure, scattering rates, and surface conditions, the present results indicate a wide margin for improvements over current performance of AlGaN/GaN HJFETs in the future. To our knowledge, this is the first report on the FBMC simulation for AlGaN/GaN HJFETs     

Enhancement-mode power heterojunction FET utilizingAl0.5Ga0.5As barrier layer with negligibleoperation gate current for digital cellular phones

We have developed a novel enhancement-mode double-doped AlGaAs/InGaAs/AlGaAs heterojunction FET (HJFET) with a 5 nm thick Al_0.5Ga_0.5As barrier layer inserted between an In _0.2Ga_0.8As channel layer and an upper Al_0.2 Ga_0.8As electron supply layer. The Al_0.5Ga _0.5As barrier layer reduces gate current under high forward gate bias voltage, resulting in a high forward gate turn-on voltage (V _F) of 0.87 V, which is 170 mV higher than that of an HJFET without the barrier layer. Suppression of gate current assisted by a parallel conduction path in the upper electron supply layer was found to be also important for achieving the high V_F. The developed device exhibited a high maximum drain current of 300 mA/mm with a threshold voltage of 0.17 V. A 950 MHz PDC power performance was evaluated under single 3.5 V operation. An HJFET with a 0.5 μm long gate exhibited 0.92 W output power and 63.6% power-added efficiency with 0.08 mA gate current (I_g) at -48 dBc adjacent channel leakage power at 50 kHz off-center frequency. This I_g is one-thirteenth to that of the HJFET without the barrier layer. These results indicate that the developed enhancement-mode HJFET is suitable for single low voltage operation power applications     

Low-operation voltage of InGaN-GaN light-emitting diodes withSi-doped In0.3Ga0.7N/GaN short-period superlatticetunneling contact layer

InGaN/GaN multiple-quantum-well light-emitting diode (LED) structures including a Si-doped In_0.23Ga_0.77N/GaN short-period superlattice (SPS) tunneling contact were grown by metalorganic vapor phase epitaxy. In_0.23Ga_0.77N/GaN(n⁺)-GaN(p) tunneling junction, the low-resistivity n⁺-In_0.3Ga_0.77 N/GaN SPS instead of high-resistivity p-type GaN as a top contact layer, allows the reverse-biased tunnel junction to form an “ohmic” contact. In this structure, the sheet electron concentration of Si-doped In_0.23Ga_0.77N/GaN SPS is around 1×10¹⁴/cm², leading to an averaged electron concentration of around 1×10²⁰/cm³. This high-conductivity SPS would lead to a low-resistivity ohmic contact (Au/Ni/SPS) of LED. Experimental results indicate that the LEDs can achieve a lower operation voltage of around 2.95 V, i.e., smaller than conventional devices which have an operation voltage of about 3.8 V     

Blue laser diodes including lattice-matched Al0.83In0.17N bottom cladding layer

A report is presented on InGaN/GaN multiple quantum well laser diodes, grown by metal organic vapour phase epitaxy on c-plane sapphire substrates, including an Al_0.83In_0.17N cladding layer lattice- matched to GaN. Lasing action is demonstrated for gain-guided devices at room temperature under pulsed current injection conditions. Direct comparison with structures including only a standard Al_0.07Ga_0.93N bottom cladding shows an improved optical confinement. This is exemplified by a decreased threshold current density.     

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     

Low-noise back-illuminated AlxGa1-xN-basedp-i-n solar-blind ultraviolet photodetectors

We report the growth, fabrication and characterization of Al_0.4Ga_0.6N-Al_0.6Ga_0.4N back-illuminated, solar-blind p-i-n photodiodes. The peak responsivity of the photodiodes is 27 and 79 mA/W at λ≈280 nm for bias voltages of 0 V and -60 V, respectively, with a UV-to-visible rejection ratio of more than three decades (at 400 nm). These devices exhibit very low dark current densities (~5 nA/cm² at -10 V). At low frequencies, the noise exhibits a 1/f-type behavior. The noise power density is S₀≈5×10^-25 A²/Hz at -12.7 V and the detectivity (D*) at 0 V is estimated to be in the range of 4×10¹¹-5×10¹³ cm·Hz^1/2 /W. Time-domain pulse response measurements in a front-illumination configuration indicate that the devices are RC-time limited and show a strong spatial dependence with respect to the position of the incident excitation, which is mainly due to the high resistivity of the p-type Al_0.4Ga_0.6 N layer     

An Al0.3Ga0.7N/GaN undoped channelheterostructure field effect transistor with Fmax of 107 GHz

An Al_0.3Ga_0.7N/GaN heterostructure field effect transistor (HFET) grown on semi-insulating SiC with an 0.2-μm gate length is reported. A source-drain ohmic contact resistance of 0.15-Ω-mm was achieved through the use of high Al content and high n-type doping (1E19 cm^-3) in the AlGaN donor layer and optimized metallization procedures. We obtained a maximum transconductance of 260 mS/mm, a saturated current density of 1.2 A/mm, and a maximum oscillation frequency in excess of 107 GHz in the devices. The results are one of the best achieved up to now, and they will open up the potential for the applications of AlGaN/GaN HFET's in high-power microwave radar, remote sensing, and communications     

32×32 ultraviolet Al0.1Ga0.9N/GaN p-i-nphotodetector array

We report the fabrication and performance of a 32×32 Al_0.1Ga_0.9N-GaN ultraviolet p-i-n photodetector array. The devices exhibit very low dark current, the mean dark current density is ~4 nA/cm² at 5-V reverse bias, and the dark current distribution is very uniform (~98% of the devices exhibit dark current density <90 nA/cm²). Owing to the design of the p-Al_0.13Ga_0.87N window layer, the external quantum efficiency is as high as 72% at 357 nm. The photocurrent distribution is also presented. The detectivity is estimated to be as high as 8×10 ¹⁴ cm·Hz^1/2·W^-1     

Al0.3Ga0.7As/GaAs HEMT's under opticalillumination

Theoretical and experimental work for the DC and RF performance of depletion mode Al_0.3Ga_0.7As/GaAs HEMTs under optical illumination is presented. The photoconductive effect increasing the 2-DEG channel electron concentration and photovoltaic effect in the gate junction are considered. Optical tuning of a 2 GHz HEMT oscillator and optical control of the gain of a 2 to 6 GHz HEMT amplifier are presented and potential applications are described     

AlxGa1−xN Ultraviolet Avalanche Photodiodes Grown on GaN Substrates

Al_xGa_1-xN (x=0.05) ultraviolet (UV) avalanche photodiodes grown on a GaN substrate are reported. The epitaxial structure was grown by metal-organic chemical vapor deposition on a free-standing bulk GaN substrate having low dislocation density. The growth conditions for Al_xGa_1-xN epitaxial layers on GaN substrates were optimized to achieve improved crystalline and structural quality. With UV illumination at lambda~250 nm, devices with mesa diameters of ~30 mum achieve stable maximum optical gains of ~50 at a reverse bias voltage of ~87 V.     

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     

Submicrometer Inversion-Type Enhancement-Mode InGaAs MOSFET With Atomic-Layer-Deposited Al2O3 as Gate Dielectric

High-performance inversion-type enhancement-mode n-channel In_0.53Ga_0.47As MOSFETs with atomic-layer-deposited (ALD) Al₂O₃ as gate dielectric are demonstrated. The ALD process on III-V compound semiconductors enables the formation of high-quality gate oxides and unpinning of Fermi level on compound semiconductors in general. A 0.5-mum gate-length MOSFET with an Al₂O₃ gate oxide thickness of 8 nm shows a gate leakage current less than 10^-4 A/cm² at 3-V gate bias, a threshold voltage of 0.25 V, a maximum drain current of 367 mA/mm, and a transconductance of 130 mS/mm at drain voltage of 2 V. The midgap interface trap density of regrown Al₂O₃ on In_0.53Ga_0.47As is ~1.4 x 10¹²/cm² ldr eV which is determined by low-and high-frequency capacitance-voltage method. The peak effective mobility is ~1100 cm² / V ldr s from dc measurement, ~2200 cm²/ V ldr s after interface trap correction, and with about a factor of two to three higher than Si universal mobility in the range of 0.5-1.0-MV/cm effective electric field.     

Double-dopedIn0.35Al0.65As/In0.35Ga0.65As power heterojunction FET on GaAs substrate with 1 W outputpower

A double-doped metamorphic In_0.35Al_0.65As/In _0.35Ga_0.65As power heterojunction FET (HJFET) on GaAs substrate is demonstrated. The HJFET exhibits good dc characteristics, with gate forward turn on voltage of 1.0 V, breakdown voltage of 20 V, and maximum drain current of 490 mA/mm. Under RF operation at a frequency of 950 MHz, a power added efficiency of 63% with associated output power of 31.7 dBm is obtained at a gate width of 12.8 mm. This large gate width and state-of-the-art power performance in metamorphic HJFETS were enabled by a selective etching, sputtered WSi gate process and low surface roughness due to an Al_0.60Ga_0.40As_0.69Sb_0.31 strain relief buffer     

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.