Device characterization of p-channel AlGaAs/GaAs MIS-like heterostructure FET's

p-channel AlGaAs/GaAs MIS-like heterostructure FET's (p-MIS HFET's) are characterized concerning their gate-source leakage current. Device performance is confirmed to improve approximately inversely to layer thickness dtbetween the channel and metal gate, at low gate voltages. A high transconductance gmof 110 ms. mm-1is obtained at 77 K by reducing dtto 20 nm. Maximum transconductance is limited by gate-source leakage current Igs. Igsis governed mainly by the leakage current through the ion-implanted gate edge and is reduced by decreasing the dose level of ion-implantation at the gate edge to 2 × 10¹³cm^-2. The contact resistance is reduced to about 0.1 ω. mm by ion implantation into the ohmic contact region to a dose of 2 × 10¹⁴cm^-2. Calculations indicate that, by reducing Igsand the gate-source resistance to 1 ω. mm with the lightly doped drain (LDD) structure, gmaround 200 mS. mm^-1at 300 K and 300 mS. mm^-1at 77 k are achievable with a 1-µm gate structure.     

High-transconductance p-channel InGaAs/AlGaAs modulation-doped field effect transistors

A p-channel quantum-well InGaAs/AlGaAs modulation-doped field effect transistor has been fabricated. With a 1-µm gate, the device exhibits transconductances of 17.8 and 89 mS/mm at room temperature and 77 K, respectively. Experimental results indicate an extrinsic transconductance greater than 200 mS/mm is achievable with reduced ohmic contact resistance and gate leakage.     

Nonlinear charge control in AlGaAs/GaAs modulation-doped FET's

A new model for nonlinear charge control in normally on modulation-doped field-effect transistors (MODFET's) is proposed. It is shown that conventional charge control models are insufficient to describe MODFET's with large negative pinchoff voltages, and that the depletion approximation is inaccurate in circumstances where the layer dimensions become of the order of a Debye length. The new model is based upon a one-dimensional numerical solution of Poisson's equation and the drift-diffusion equation. It also takes into account the shift in the 2DEG position with gate bias, and parallel conduction in the doped AlGaAs layer. The effect of nonlinear charge control on MODFET transconductance is considered by combining the new model with a two-dimensional analytic representation of the MODFET.     

Characterization of deep levels in modulation-doped AlGaAs/GaAs FET's

Deep levels in modulation-doped field-effect transistors (MODFET's) fabricated from MBE-grown AlGaAs/GaAs heterostructures, have been characterized by a modified deep-level transient spectroscopy (DLTS) technique. Assuming donor-like traps in the AlGaAs layer, it is shown that the threshold voltage Vtvaries exponentially with time under pulsed-biased conditions. This result is verified experimentally by observing the transient in the drain current IDin long-gate FET's biased in saturation. The resulting Δ √{I_{D}} DLTS spectrum reveals an electron trap with an activation energy of 0.472 eV in Si-doped Al0.3Ga0.7As.     

High-transconductance p-channel AlGaAs/GaAs HFETs with low-energyberyllium and fluorine co-implantation self-alignment

The fabrication and electrical characteristics of p-channel AlGaAs/GaAs heterostructure FETs with self-aligned p⁺ source-drain regions formed by low-energy co-implantation of Be and F are reported. The devices utilize a sidewall-assisted refractory gate process and are fabricated on an undoped AlGaAs/GaAs heterostructure grown by MOVPE. Compared with Be implantation alone, the co-implantation of F⁺ at 8 keV with 2×10¹⁴ ions/cm² results in a 3× increase in the post-anneal Be concentration near the surface for a Be⁺ implantation at 15 keV with 4×10¹⁴ ions/cm². Co-implantation permits a low source resistance to be obtained with shallow p⁺ source-drain regions. Although short-channel effects must be further reduced at small gate lengths, the electrical characteristics are otherwise excellent and show a 77-K transconductance as high as 207 mS/mm for a 0.5-μm gate length     

Interface states of modulation-doped AlGaAs/GaAs heterostructures

We have used the admittance spectroscopy to investigate interface states associated with heterojunction of modulation-doped AlGaAs/GaAs FET's. Anomalous frequency dispersion of the capacitance was observed. The results of the measurements were interpreted in terms of an equivalent circuit containing a series resistance of the two-dimensional electron gas in the ungated region between the gate and the source and drain electrodes. The maximum density of the interface states was found to be 1.3 × 10¹²cm^-2. eV^-1around 0.13 eV below the Ecedge of GaAs.     

Demonstration of a p-channel GaAs/AlGaAs BICFET

The p-channel bipolar inversion-channel field-effect transistor (BICFET) is a bipolar transistor which utilizes an inversion layer induced by planar doping using molecular beam epitaxy. A current gain of ~8 is obtained at a current density of ~8×10³ A/cm². The results agree well with previous theoretical predictions of current gain, output conductance, and collector offset voltage. There is no base transit time in the BICFET and thus the speed of the device will be determined by transit-time-limited transport in the collector     

Ion-implanted GaAs/AlGaAs heterojunction FET's grown by MOCVD

The successful fabrication of an ion-implanted GaAs/AlGaAs heterojunction FET device is discussed. Half-micrometer gate-length FET devices are fabricated by ion implantation into GaAs/AlGa heterostructures grown by metalorganic chemical vapor deposition (MOCVD) on 3-in-diameter GaAs substrates. The FET device exhibits a maximum extrinsic transconductance of 280 mS/mm with reduced transconductance variation over 2 V of gate bias. Excellent microwave performance is achieved with an f_t of 40 GHz, which is comparable to results obtained from 0.25-μm gate GaAs MESFETs. The effects of ion implantation on the heterojunction and corresponding device characteristics are also discussed     

AlGaAs/GaAs 2-DEG FET's fabricated from MO-CVD Wafers

A transconductance (gm) of as high as 330 mS/mm is obtained from wafers grown by MO-CVD in which triethyl gallium and triethyl aluminum are used as organometallic compounds. A comparison between the experimental and theoretical results is made for the dependence of gmon the thickness of the AlGaAs layer. The saturation of velocity of 2-DEG determined from the drain I-V characteristics is found to be as high as 2 × 10⁷cm/s regardless of the absence of the undoped spacer layer.     

Modulation-doped AlGaAs/GaAs heterostructure charge coupled devices

The advantages of the modulation-doped heterostructure over conventional materials structures for high speed CCD applications are outlined. In addition, the first demonstration of charge transfer in a modulation-doped AlGaAs/GaAs heterojunction is reported. A ten cell, three phase Schottky barrier gate CCD was fabricated using this structure and operated as a shift register. The details of the device fabrication and characterization are presented.     

Characteristics of AlGaAs/GaAs heterostructure RT-SCR model

Electrical properties of a resonant-tunneling-semiconductor-controlled rectifier (RT-SCR) model have been presented. The current, temperature, gain, doping concentration, and layer size versus voltage relationships have been numerically obtained. The RT-SCR device requires smaller turn-on voltage than a comparable traditional device for the same gate current. This indicates that, in comparison with the traditional thyristor, a smaller control current may be used to turn on the device at a particular voltage. Characteristics of the device are affected by p1, n1, and p2 regions. It is showed that higher doping concentrations cause lower turn-on voltages and an increase in the region width results in higher turn-on voltages for p1 and p2 regions. Changing the doping concentration and width in n1 region affects the characteristics of the structure differently from that of the p1 and p2 regions.     

n+ self-aligned-gate AlGaAs/GaAs heterostructure FET

The n+ self-aligned-gate technology for high-performance AlGaAs/GaAs heterostructure FETs employing rapid lamp annealing have been studied. The large transconductance of 330 mS/mm at 300 K and 530 mS/mm at 83 K was obtained for the 0.7 ?m gate length device, by reducing the source resistance to 0.6 ?mm. The minimum delay time of 18.7 ps was obtained with a power dissipation of 9.1 mW at 300 K. The standard deviation of the delay time was as small as 1.1 ps at a fixed bias of 2.5 V.     

AlGaAs/InGaAs heterostructure doped-channel FET's exhibiting goodelectrical performance at high temperatures

High-power and high-efficiency GaAs heterostructure field-effect transistors (FETs) are attracting tremendous attention in RF power amplifier applications. However, thermal effects can be an important issue in RF power devices, owing to the huge amount of heat generated during their operation. In this paper, the temperature-dependent characteristics of Al_0.3Ga_0.7As/In_0.15Ga_0.85 As doped-channel FETs (DCFETs) are investigated and compared with conventional pseudomorphic-HEMTs (pHEMTs) devices, in terms of their dc, microwave and RF power performance at temperatures ranging from room temperature to 150°C. Due to conducting carriers being less influenced by temperature and the better Schottky diode characteristics that can be obtained in DCFETs, the intrinsic device parameters and output performance remain almost constant at high temperatures, which also results in better device reliability. The performance variation of DCFETs associated with temperatures from 25°C to 150°C all fall within a single digit, i.e., output power (P_out, 16.2 dBm versus 15.8 dBm), power gain (G_p, 16.6 dB versus 15.1 dB), power added efficiency (PAE, 34.2% versus 31.3%), which is not the case for conventional pHEMTs. Therefore, DC devices are very promising for microwave power device applications operating at high temperature     

High-transconductance n-type Si/SiGe modulation-doped field-effecttransistors

The authors report on the fabrication and the resultant device characteristics of the first 0.25-μm gate-length field-effect transistor based on n-type modulation-doped Si/SiGe. Prepared using ultrahigh vacuum/chemical vapor deposition (UHV/CVD), the mobility and electron sheet charge density in the strained Si channel are 1500 (9500) cm²/V-s and 2.5×10¹² (1.5×10¹² ) cm^-2 at 300 K (77 K). At 77 K, the devices have a current and transconductance of 325 mA/mm and 600 mS/mm, respectively. These values far exceed those found in Si MESFETs and are comparable to the best results achieved in GaAs/AlGaAs modulation-doped transistors     

AlGaAs/GaAs bipolar transistors with a modulation-doped superlattice emitter

A new emitter-base concept for heterojunction bipolar transistors is proposed and demonstrated. The abrupt or graded emitter-base heterojunction drawbacks are circumvented by means of a modulation-doped stack of ternary compound alternating with binary compound layers. This stack provides efficient barriers to the hole current while preserving good diode characteristics. These concepts are demonstrated by experimental results on small-area devices with a common-emitter gain of ~40 and a collector-emitter voltage offset of ~80mV.     

Studies of high-speed metal-semiconductor-metal photodetector witha GaAs/AlGaAs/GaAs heterostructure

A GaAs/AlGaAs/GaAs heterostructure metal-semiconductor-metal photodetector (HMSM) with an active area of 100 μm×100 μm was developed and studied. The measured risetime of the device is 30 ps. The measured falltime is as short as 23 ps. The observed ultrafast response is attributed to the reduction of both the carrier transit time and the device capacitance due to the incorporation of the AlGaAs barrier layer. The HMSM is found to have a smaller saturation capacitance and saturates at a much lower bias voltage in comparison with the conventional MSM photodetector (CMSM). At a bias of 10 V, the full width at half maximum (FWHM) of the temporal response of the HMSM is more than 20% smaller than that of the CMSM. In addition, it is found that the peak impulse response for the HMSM is substantially larger than that of the CMSM under the same operation condition. Two-dimensional and equivalent circuit analyses were carried out to interpret the observed phenomena and to provide insight into the underlying physics     

GaAs/AlGaAs异质结的微波调制反射谱

基于搭建的微波调制反射谱测量系统(MMRS),确定了GaAs/AlGaAs异质结构中价带空穴到二维电子系统(2DES)电子基态(GS)的跃迁.微波调制反射谱与温度的依赖关系表明,随着测量温度的升高,能带带隙发生了蓝移现象;而其与磁场的依赖关系表明,随着测量磁场的增大,能带带隙则发生了红移现象;它们均与GaAs/AlGa...     

Low-temperature degradation studies of AlGaAs/GaAs modulation-doped field effect transistors

The degradation of AlGaAs/GaAs modulation-doped field effect transistors (MODFETs) was studied at the low temperature of 77 K. The MODFETs were stress tested at 77 K under both short- and long-term bias stress conditions. The measured MODFET parameters include threshold voltage V_t, transconductance g_m and the gate voltage V_u at which g_m shows a maximum. Shifts of V_t, g_m and V_u were studied as a function of stress voltage and stress time. The measured shifts are found to depend on (V_g − V_d) which indicates the influence of hot electrons coming from the high mobility channel. The MODFETs were also tested for temperature cycling between 300 and 77 K up to 20 cycles. Some changes of device properties at 77 K were observed.     

Inverted GaAs/AlGaAs modulation-doped field-effect transistors with extremely high transconductances

Inverted GaAs/AsGaAs MODFET's with transconductances as high as 1810 mS/mm at 77 K and 1180 mS/mm at 300 K are fabricated using a self-aligned process. The devices have the gate-heterojunction interface spacing of only 100 Å, and the observed values of the transconductance are limited primarily by the source series resistance and by the gate current. The MODFET characteristics are interpreted using the charge control velocity saturation model which takes into account the gate current. The obtained results show a great potential of inverted MODFET's for ultrahigh-speed applications.     

Realization of n-channel and p-channel high-mobility (Al,GA)As/GaAs heterostructure insulating gate FET's on a planar wafer surface

Self-aligned gate by ion implantation n-channel and p-channel high-mobility (Al,Ga)As/GaAs heterostructure insulated-gate field-effect transistors (HIGFET's) have been fabricated on the same planar wafer surface for the first time. Enhancement-mode n-channel (Al,Ga)As/GaAs HIGFET's have demonstrated extrinsic transconductances of 218 mS/mm at room temperature and 385 mS/mm at 77 K. Enhancement-mode p-channel (Al,Ga)As/GaAs HIGFET's have demonstrated extrinsic transconductances of 28 mS/mm at room temperature and 59 mS/mm at 77 K. There are the highest transconductance values ever reported on a p-channel FET device.