Characterization of the frequency dispersion of transconductance and drain conductance of GaAs MESFET

Frequency dispersions of the transconductance and the drain conductance of ion-implanted gallium arsenide (GaAs) metal-semiconductor field-effect transistors (MESFETs) are measured and analyzed. In the linear region of the MESFET (low drain voltage), a positive transconductance dispersion is observed, which is caused by the deep-level traps at the surface between the source and the gate. In the saturation region (high drain voltage), however, a negative transconductance dispersion becomes dominant. The drain conductance does not show a dispersion in the linear region, while a distinct positive dispersion is observed in the saturation region with the same activation energy as the negative transconductance dispersion. The difference of the dispersion activation energy of the MESFET with and without the p-buried layer beneath the channel indicates that the negative transconductance and the drain conductance dispersion are caused by the deep-level traps at the channel-substrate interface. Because there exists the high electric field at the drain edge of the gate and an electron accumulation layer is formed, the potential in the channel becomes lower when the drain current is larger with high gate voltage. The emission of electrons from electron traps with lower potential is the cause of the negative frequency dispersion.     

Experimental correlation between substrate properties and GaAs MESFET transconductance

The relationship between the characteristics of FET's obtained by direct ion implantation and the properties of a GaAs semi-insulating substrate was investigated. A positive correlation was observed between the dislocation etch-pit density, the as-grown mobility, the mobility after implantation, and the device transconductance. The observation of dislocations' effect on mobility is consistent with the model that dislocations act as segregation centers for imperfections. Localized substrate inhomogeneties are shown to affect the GaAs FET's frequency performance via the mobility.     

Submicrometer GaAs MESFET with shallow channel and very high transconductance

A 0.5-µm GaAs MESFET with a 25-nm thin channel, 400- mS/mm maximum transconductance, and 580-mS/V.mm K value is presented. This extremely high K value was obtained using an electron-beam fabricated recessed-gate MESFET structure on a highly doped (9.10¹⁷cm^-3) MBE-grown channel layer with 2600-cm²/V.s mobility. The use of thin channels and a buried p-layer also reduced the output conductance and other short-channel effects dramatically. As a result, these scaled MESFET's are very promising for high-speed digital logic circuits.     

Deep level transient spectroscopy of n-AlGaAs/GaAs high electron mobility transistors

Deep level transient spectroscopy has been used to characterise the traps found in MBE grown n-AlGaAs/GaAs HEMTs. In addition to DX centres two further traps common to different HEMT structures are reported. The authors have identified an electron trap (E/sub a/=0.6 eV) distributed nonuniformly in the AlGaAs donor layer, and an interface state trap (E/sub a/=0.55 eV) located close to the two dimensional electron gas.<>     

Low-frequency dispersion of transconductance in GaAs JFETs andMESFETs with an ion-implanted channel layer

An analytical model of low-frequency dispersion of transconductanced in GaAs FETs which have nonuniform profiles of carrier concentration and mobility is reported. The frequency dependence of surface charge density is incorporated into the model as a variation in the source resistance of the FETs. The model explains the low-frequency dispersion of transconductance in GaAs p-n junction FETs (JFETs) and metal-semiconductor FETs (MESFETs), both of which have a channel layer formed by ion implantation. It is suggested that the low-frequency dispersion of transconductance can be attributed to the charge exchange which occurs with the surface states in GaAs FETs     

A transconductance spectroscopy approach to device level surfacestate characterization

A device level transconductance spectroscopy approach is developed for characterizing surface states in metal-semiconductor field-effect transistors. A comparison of the theoretical results and the available experimental observations shows that the model can successfully explain both the surface leakage current dependence of transconductance dispersion magnitude reported by M. Ozeki et al. (1982) and the temperature dependence of transconductance dispersion observed by S.R. Blight et al. (1986)     

Trap studies in GaInP/GaAs and AlGaAs/GaAs HEMT's by means oflow-frequency noise and transconductance dispersion characterizations

The presence of traps in GaInP/GaAs and AlGaAs/GaAs HEMT's was investigated by means of low frequency noise and frequency dispersion measurements. Low frequency noise measurements showed two deep traps (E _a1=0.58 eV, E_a2=0.27 eV) in AlGaAs/GaAs HEMT's. One of them (E_a2) is responsible for the channel current collapse at low temperature. A deep trap (E_a1'=0.52 eV) was observed in GaInP/GaAs HEMT's only at a much higher temperature (~350 K). These devices showed a transconductance dispersion of ~16% at 300 K which reduced to only ~2% at 200 K. The dispersion characteristics of AlGaAs/GaAs HEMT's were very similar at 300 K (~12%) but degraded at 200 K (~20%). The low frequency noise and the transconductance dispersion are enhanced at certain temperatures corresponding to trap level crossing by the Fermi-level. The transition frequency of 1/f noise is estimated at 180 MHz for GaInP/GaAs HEMT's and resembles that of AlGaAs/GaAs devices     

Distributed effect in GaAs MESFET

In order to obtain higher output power, the width of a single cell MESFET must be large. When it becomes too large the distributed effect along the width direction tends to limit the output power. In this paper, we found that the distributed effect is important when the gate width ≥ 150 μ and that the gain decreases with gate width. Also found is that spurious oscillations occur due to line resonances at much higher frequencies than can be accounted for by the instability factor in the discrete device model.     

Accurate measurement of capture cross sections in deep level transient spectroscopy: Application to EL2 in GaAs

A rigorous formulation of capacitance changes during trap filling processes is presented and used to accurately determine the electron capture cross section of EL2 in GaAs at a particular temperature, 377K, in this case. The value, σ_n (377K) = 2.7 × 10⁻¹⁶ cm², is compared with that predicted from the emission dependence.     

Realisation of very high transconductance GaAs MESFETs

By using a model which considers velocity overshoot, it is shown that the performance of GaAs MESFETs in enhancement mode depends strongly on the geometrical and electrical characteristics of the access region between source and gate. The sheet resistance of the unrecessed epilayer, and the distance between the source-end of the recessed region and the gate, have to be as small as possible. 300 nm gate length MESFETs with very low values for these parameters were realised with an n-GaAs active layer (6×10¹⁷ cm^-3). These devices exhibit very high microwave transconductances (800 mS/mm) with good cutoff frequencies (up to 55 GHz). This result suggests that very high transconductance MESFETs can be fabricated from not-too-heavily doped active layers provided that the characteristics of the source-gate access region is properly optimised     

GaAs MESFET开关模型

本文提出了一种MESFET开关的模型———附加栅控开关模型 ,适用于MMIC电路的设计 ,其具有很好的宽带微波特性。开关单片的设计值与模型模拟值吻合较好。     

Some Aspects of GaAs MESFET Reliability

The results of a short study into the reliability and failure modes of GaAs MESFET's are presented. Two failure modes have been observed during this study and improved fabrication techniques that reduce their occurrence have been examined. The results obtained indicate that extremely reliable devices can be manufactured with a predicted mean time to failure in excess of 10/sup 7/ h at junction temperatures of 70/spl deg/C. Room-temperature life tests in excess of 1/2 million device hours lend support to these predictions.     

GaAs MESFET低温性能实验

本文介绍了在低温下,对GaAs MESFET(包括12GHz低噪声器件、双栅器件、功率器件及振荡用器件)所进行的性能测量与分析。在218K(-55℃)下,上述各类器件的跨导g_m相对于室温可增加5～8％,器件的C_(gs)可减少20～50％,器件的寄生电阻R_s和R_d可减少15～40％,R_g也存在缓慢下降的趋势。 文章还给出了低温下低噪声GaAs MESFET放大器的噪声、增益—温度曲线。在218K下,放大器的噪声相对室温可下降1dB左右,单级增益相对室温可增加1～1.5dB,即在低温表现出良好的微波性能。     

Comparison of GaAs MESFET noise figures

A method of comparing noise figures of GaAs MESFET's is presented. The noise measure M graphed against gate length for devices having the lowest value of M gives a figure of merit graph against which other devices may be compared. This is useful in determining the relative value of material and process, improvements for a given gate length.     

S-parameter model of dual-gate GaAs MESFET

A simple modelling procedure for the dual-gate MESFET is presented. The model is based on a cascoded connection of two single-gate devices, with each device represented in terms of its s-parameters. These s-parameters are obtained from the overall dual-gate MESFET s-parameters, using accurate deembedding techniques.     

Electrical characterization of self-assembled In0.5Ga0.5As/GaAs quantum dots by deep level transient spectroscopy

We have investigated electron emission from self-assembled In_0.5Ga_0.5As/GaAs quantum dots (QDs) grown by molecular-beam epitaxy (MBE). Through detailed deep level transient spectroscopy comparisons between the QD sample and a reference sample, we determine that trap D, with an activation energy of 100 meV and an apparent capture cross section of 5.4×10⁻¹⁸ cm², is associated with an electron quantum level in the In_0.5Ga_0.5As/GaAs QDs. The other deep levels observed, M1, M3, M4, and M6, are common to GaAs grown by MBE.     

硫钝化GaAs MESFET的机理研究

研究了硫钝化对GaAs MESFET直流特性的影响,并通过对钝化前后击穿电压的分析,认为负电荷表面态的增加减弱了栅靠漏一侧的电场强度,是导致器件击穿电压升高的原因.     

Analysis of kink-related backgating effect in GaAs MESFET

Two-dimensional simulation of backgating effect in a GaAs MESFET is made in which impact ionization of carriers and deep donors “EL2” in the substrate are considered. The kink-related backgating is reproduced, which is qualitatively consistent with recent experiments. Based on the simulated results, physical mechanism of kink-related backgating effect is discussed     

Threshold voltage of ion implanted GaAs MESFET

Threshold voltages for ion implanted GaAs MESFETs are measured and shown to have good coincidence with calculated results. The effect of implantation energy on threshold voltage is discussed. The optimum implantation energy is about 45 ~ 60 keV.     

宽带GaAs三栅MESFET开关模型

提出一种三栅MESFET开关的模型--附加栅控开关模型,模型是根据三栅MESFET开关器件的结构,考虑了栅极对微波信号的影响,适用于MMIC开关电路的设计,具有很好的宽带微波特性.器件测试值与模型模拟值吻合较好.