Effects of RF life-test on LF electrical parameters of GaAs power MESFETs

Ion-implanted power MESFETs have been submitted to RF life-test under gain compression. Devices went through RF life-test with no significant dynamic performance drift but with DC parameter evolution. A complete electrical characterisation performed by low frequency gate and drain noise analysis combined with drain current transient spectroscopy revealed that no degradation has occurred in the channel. An increase by two orders of magnitude of the LF gate noise level points out a degradation located in the vicinity of the gate.     

Numerical analysis of the photoeffects in GaAs MESFET's

The photoeffects on the I-V characteristics of GaAs MESFETs have been studied by a two-dimensional numerical method. It is theoretically verified that the photovoltaic effect occurring at the channel/substrate interface is responsible for the substantial increase of the drain current. The reverse gate current due to illumination is caused by sweep-out by the high electrical field in the gate depletion region, where a large gradient in the depth profile of the hole Fermi energy is found. For devices with a lightly doped n-type buffer layer, the increase of the drain current is less than for devices without a buffer layer, but is still substantial     

Low-frequency noise properties of selectively dry etched InP HEMT's

The low-frequency noise of lattice-matched InAlAs/InGaAs/InP high electron mobility transistors (HEMT's) gate recess etched with a highly selective dry etching process and with conventional wet etching were studied at different gate and drain biases for the temperature range of 77-340 K. The measurements showed a significantly lower normalized drain current 1/f noise for the dry etched HEMT's under all bias conditions. No difference in the normalized gate current 1/f noise could be observed for the two device types. By varying the temperature, four electron traps could be identified in the drain current noise spectra for both dry and wet etched devices. No additional traps were introduced by the dry etching step. The concentration of the main trap in the Schottky layer is one order of magnitude lower for the dry etched HEMT's. No hydrogen passivation of the shallow donors was observed in these devices. We presume hydrogen passivation of the deep levels as the cause for the trap density reduction. The kink effect in the dry etched HEMT's was observed to be reduced significantly compared with wet etched devices which gives further evidence of trap passivation during dry etching. These results show that dry etched InP HEMT's have suitable characteristics for the fabrication of devices for noise sensitive applications     

High DC and microwave characteristics of subhalf-micrometre gate ion-implanted GaAs MESFETs using trilayer deep UV lithography

Subhalf-micrometre gate length ion-implanted GaAs MESFETs have been fabricated on 3 inch diameter substrates using trilayer deep UV lithography. Implanted MESFETs with 0.3 mu m gate lengths exhibit a maximum extrinsic transconductance of 205 mS/mm at a drain current of 600 mA/mm. From S-parameter measurements, a current gain cutoff frequency f/sub t/ of 56 GHz and a maximum available gain cutoff frequency f/sub max/ greater than 90 GHz are achieved. The gate-to-drain diode characteristics of the devices show a sharp breakdown voltage of 13-15 V. The high drain current-drain voltage and microwave characteristics indicate that ion-implanted technology with trilayer deep UV lithography has potential for the manufacture of power devices and amplifiers for Q-band communication applications. This is the first reported result using trilayer deep UV lithography to demonstrate both f/sub t/ over 56 GHz and 13-15 V gate-to-drain breakdown on 0.3 mu m gate-length ion-implanted GaAs MESFETs.<>     

Noise modeling for RF CMOS circuit simulation

The RF noise in 0.18-/spl mu/m CMOS technology has been measured and modeled. In contrast to some other groups, we find only a moderate enhancement of the drain current noise for short-channel MOSFETs. The gate current noise on the other hand is more significantly enhanced, which is explained by the effects of the gate resistance. The experimental results are modeled with a nonquasi-static RF model, based on channel segmentation, which is capable of predicting both drain and gate current noise accurately. Experimental evidence is shown for two additional noise mechanisms: 1) avalanche noise associated with the avalanche current from drain to bulk and 2) shot noise in the direct-tunneling gate leakage current. Additionally, we show low-frequency noise measurements, which strongly point toward an explanation of the 1/f noise based on carrier trapping, not only in n-channel MOSFETs, but also in p-channel MOSFETs.     

Bias dependence of low-frequency gate current noise in GaAs MESFETs

The spectra of gate current noise are investigated in GaAs MESFETs between 10/sup 2/ and 10/sup 4/ Hz. A change in the white-noise behaviour is observed with the increase of the gate current. It is shown that the contribution of an ideal Schottky shot noise is associated with two thermal noise components. The thermal noise sources originate in different leakage conductances.<>     

Enhanced microwave performance of ion-implanted MESFET with graded GaAs/AlGaAs heterojunctions

Ion-implanted MESFETs have been fabricated on an inverted GaAs/AlGaAs heterostructure. The aluminium concentration in the AlGaAs is graded from 0% at the substrate to 30% at the heterointerface. A maximum extrinsic transconductance of 410 mS/mm is achieved with 0.5 mu m gate devices. This heterojunction ion-implanted FET (HIFET) also exhibits enhanced microwave performance, especially at low drain current, when compared to conventional ion-implanted GaAs MESFETs. At 20% of I/sub dss/, the current gain cutoff frequency f/sub t/ is 40 GHz, which increases up to a maximum value of 47 GHz as the drain current rises. These characteristics of high f/sub t/ and high gain at low current are advantageous for low-noise applications.<>     

Nonlinear GaAs MESFET modeling using pulsed gate measurements

The effects of traps in GaAs MESFETs are studied using a pulsed gate measurement system. The devices are pulsed into the active region for a short period (typically 1 μs) and are held in the cutoff region for the rest of a 1-ms period. While the devices are on, the drain current is sampled and a series of pulsed gate I-V curves are obtained. The drain current obtained under the pulsed gate conditions for a given V_GS and V_DS gives a better representation of the instantaneous current for a corresponding V_gs and V_ds in the microwave cycle because of the effects of traps. The static and pulsed gate curves were used in a nonlinear time-domain model to predict harmonic current. The results showed that analysis using pulsed gate curves yielded better predictions of harmonic distortion than analysis based on conventional state I-V curves under large-signal conditions     

Origins and characterization of low-frequency noise in GaAsMESFET's grown on InP substrates

An experimental study of the low-frequency noise in GaAs MESFET's grown on InP substrates is reported. The influence of the biases applied to the gate, backgate, and drain in the ohmic region is investigated in order to identify and characterize the 1/f noise origin. We find that this noise can be explained by carrier number fluctuations in the channel and related to trapping phenomena. The traps responsible for this noise are located near the channel-buffer interface. Moreover, the noise behavior exhibits for a well-defined gate voltage, corresponding to the case where the drain current flows near the channel-buffer interface, a GR-type (Lorentzian) noise spectrum emerging from a quite general 1/f noise. This last spectrum corresponds to a single trap level with a density of N_T=10¹⁶ cm^-3 and a time constant τ=1.8 ms which may be attributed to crystal defects present in the GaAs layers     

Experimental and theoretical noise analysis of microwave HEMTs

Low-frequency noise power and high-frequency noise figures in HEMTs (high electron mobility transistors) were measured and compared with calculations based on a one-dimensional noise model to characterize their low-noise properties. It was found that the drain noise current parameter Q in HEMTS is lower than that in GaAs MESFETs. The strong correlation between drain- and induced-gate-noise currents in HEMTs is due to the asymmetric distribution of noise generation along a channel, and the drain noise current is nearly canceled by those induced-gate-noise current. The intrinsic thermal noise from source and gate resistances is about 25% of the total output noise in the 0.25-μm gate-length HEMT considered     

Empirical modeling of LF gate noise in GaAs DCFET in impactionization regime

The evolution of the 1/f gate noise in GaAs DCFET has been analyzed in the impact ionization regime. As the drain bias Vd is raised, a steep increase of the 1/f gate current noise is observed in correlation with the triggering of the impact ionization mechanism. A novel and empirical model of the 1/f low frequency gate current noise S _ig measured in the impact ionization regime is proposed. The following relation fits it with an exponential law: S_ig=E exp (-F/Vd) (1/f), which is similar to the well-known dependence of the impact ionization rate α on the drain bias     

4H-SiC MESFET's with 42 GHz fmax

We report for the first time the development of state-of-the-art SiC MESFETs on high-resistivity 4H-SiC substrates. 0.5 μm gate MESFETs in this material show a new record high f_max of 42 GHz and RF gain of 5.1 dB at 20 GHz. These devices also show simultaneously high drain current, and gate-drain breakdown voltage of 500 mA/mm, and 100 V, respectively showing their potential for RF power applications     

Effect of Schottky barrier alteration on the low-frequency noise ofInP-based HEMTs

For the first time the effect of increasing the Schottky barrier's Al content of InP-based InAlAs-InGaAs HEMTs from 48 to 60% on the low-frequency (LF) drain and gate current noise is investigated. It is shown that the LF gate current noise S_IG(f) for the 60% case decreases by almost three decades, while the LF drain current noise S _IDS(f) stays at the same level. From small coherence values, it can be concluded that drain and gate noise sources can be treated separately which facilitates the LF noise modeling of these HEMTs     

n型GaAs MESFET沟道特性的研究

报道了ｎ型ＧａＡｓ ＭＥＳＦＥＴ漏源电流Ｉｄｓ和栅源电压Ｖｇｓ间的关系,发现在负栅压状态下,沟道特性分四个区域：过调制区、线性调制区、过渡区和夹断区,并且零栅压饱和漏源电流大的器件线性调制区的范围较大,过渡区的范围较小。     

电应力对GaAlAs红外发光二极管低频噪声的影响

在宽范围偏置条件下,测量了电应力前后GaAlAs红外发光二极管（IRED）的低频噪声,发现应力前后1／f噪声随偏置电流变化的规律没有改变,但应力后1／f噪声幅值比应力前增加大约i00倍。基于载流子数和迁移率涨落的理论分析表明,GaAlAs IRED的1／f噪声在小电流时反映体陷阱特征,大电流时反映激活区陷阱特征,1／f噪声的增加归因于电应力在器件有源区诱生的界面陷阱和表面陷阱,因而,1／f噪声可以用来探测电应力对该类器件有源区的潜在损伤。     

Improved double-recessed 4H-SiC MESFETs structure with recessed source/drain drift region

An improved double-recessed 4H-SiC MESFETs structure with recessed source/drain drift region was proposed. The recessed source/drain drift region is to reduce channel thickness between gate and drain as well as eliminate gate depletion layer extension to source/drain. The recessed source/drain drift region of the proposed structure can be realized with the formation of double-recessed gate region. The simulated results showed that the breakdown voltage of the proposed structure is 145 V compared to 109 V of that of the published 4H-SiC MESFETs with double-recessed gate structure and yet maintain almost same saturation drain current characteristics. The output power density of the proposed structure is about 33% larger than that of the published double-recessed gate structure. The cut-off frequency (f_T) and the maximum oscillation frequency (f_max) of the proposed structure are 21.8 GHz and 81.5 GHz compared to 19.0 GHz and 76.4 GHz of that of the published double-recessed gate structure, respectively.     

Light emission of GaAs power MESFETs under RF drive

Light emission from microwave power GaAs MESFETs was observed under rf operating conditions. It is shown that the light emission occurs at the drain side of the gate stripe and the light intensity can be correlated with the rf input drive and the output power saturation characteristic of the device.     

Fabrication and characterization of 4H-SiC planar MESFETs

The planar 4H-SiC MESFETs were fabricated by employing an ion-implantation process instead of a recess gate etching process, which is commonly adapted in compound semiconductor MESFETs, to eliminate potential damage to the gate region during etching process. Excellent ohmic and Schottky contact properties were achieved by using the modified RCA cleaning of 4H-SiC surface and the sacrificial thermal oxide layer. The fabricated MESFETs was also free from drain current instability, which the most of SiC MESFETs have been reported to suffer for the charge trapping. The drain current recovery characteristics were also improved by passivating the surface with a thermal oxide layer and eliminating the charge trapping at the surface. The performance of fabricated MESFETs was characterized by analyzing the small-signal equivalent circuit parameters extracted from the measured parameters.     

TiA1和TiPtAu栅GaAs MESFET稳定性研究

在高温和大栅电流下 ,对 Ti Al栅和 Ti Pt Au栅 MESFET的稳定性进行了比较研究 ,结果表明 :( 1)两种器件的击穿电压稳定 ,栅 Schottky接触二极管理想因子 n变化不明显 ;( 2 ) Ti Al栅的 MESFET的栅特性参数 (栅电阻 Rg,势垒高度 Φb)变化明显 ,与沟道特性相关的器件参数 (如最大饱和漏电流 Idss,栅下沟道开路电阻 R0 ,夹断电压 Vp0 等 )保持相对不变 ;( 3)对 Ti Pt Au栅MESFET来说 ,栅 Schottky二极管特性 (栅电阻 Rg,势垒高度 Φb)保持相对稳定 ,与沟道特性相关的器件参数 (如最大饱和漏电流 Idss,栅下沟道开路电阻 R0 ,夹断电压 Vp0 、跨导 gm 等 )明显变化 ,适当退火后 ,有稳定的趋势。这两种器件的参数变化形成了鲜明的对比。     

A physically based small-signal circuit model for heterostructureacoustic charge transport devices

A physically based small-signal circuit model for GaAs-AlGaAs Schottky gate heterostructure acoustic charge transport (HACT) devices is presented. Analytical expressions for the instantaneous and average channel current as a function of gate voltage are obtained from physical device parameters. The charge injection model is based on subthreshold current models for GaAs MESFETs. It is shown that the shape of the sampling aperture of the charge injection operation is approximately Gaussian. Good agreement is obtained between the measured DC channel current versus gate voltage and that predicted by the model. Equivalent circuits for the transfer and output sensing operations and expressions for noise sources due to the physical processes that occur within the device are developed. Thermal, shot, and transfer noise are treated. The form of the analytic expressions for frequency response and noise figure allows easy implementation on commercially available CAE software. Simulations of both gain and noise figure performed on Libra show good agreement with measured data