Analysis and modelling of lateral heterostructure field-effect bipolar transistors

Lateral heterostructure field-effect bipolar transistors (LH-FEBTs) are thin-film transistors that have a distinct heterojunction located roughly midway between the source and drain contacts, with a p-type semiconductor on one side of the junction, and an n-type semiconductor on the other. These devices have potential in display applications but are relatively new to the research community. In this paper, we describe the fabrication of a hybrid LH-FEBT using pentacene and ZnO as the p- and n-type semiconductors, respectively, and describe its unusual bell-shaped electrical transfer characteristics. Using an equivalent circuit approach, we analyse quantitatively how the main features of the current–voltage curves relate to semiconductor properties such as carrier mobility and threshold voltage – information that is essential to the design of such devices.     

Gate leakage current in GaN-based mesa- and planar-type heterostructure field-effect transistors

The excessive gate leakage current of the planar- and mesa-type InAlN/GaN heterostructure field-effect transistors (HFETs) is evaluated. It is found that the gate current of the mesa-type HFETs is higher than that of the planar devices, particularly at low biases. Analyses of the gate current considering different transport mechanisms yielded identical thermionic currents (i.e., an identical Schottky barrier height) but a significantly higher leakage component in the mesa-type HFETs than in the planar devices. This additional current component observed in the mesa-type devices shows a nearly ohmic behavior. Mapping by the electron-beam induced current technique confirms an enhanced current located under the expanded gate contact and on the part of the mesa-sidewall, where the gate contact is placed. Two-dimensional simulation of the device structure shows that considerable part of the gate leakage current flows through the GaN buffer layer. These results underline the importance of a proper design of the device structure and layout (i.e., the use of planar structure with device insulation prepared by ion implantation rather than by mesa technique), and of the preparation of the GaN buffer (it should be semi-insulating) in order to fabricate reliable, low leakage current GaN-based HFETs.     

New mechanism of gate current in heterostructure insulated gate field-effect transistors

We demonstrate that the mechanism responsible for the gate current in heterostructure insulated gate field-effect transistors (HIGFET's) changes drastically at the gate voltage equal to the threshold voltage. At the gate voltages below the threshold voltage the gate current is determined by the thermionic emission over the Schottky barrier at high temperatures and by the thermionic field emission at low temperatures. Above the threshold the gate current is determined by the new mechanism which is the thermionic emission over the conduction band discontinuity at high temperatures and by tunneling through the AlGaAs layer at low temperatures. We present the model describing the gate current in the entire range of the gate voltages and device temperatures.     

Analysis of surface-state and impact-ionization effects on breakdown characteristics and gate-lag phenomena in narrowly recessed gate GaAs FETs

Effects of surface states and recess structures on breakdown characteristics of GaAs MESFETs are studied by two-dimensional (2-D) analysis. It is shown that the breakdown voltage could be raised when moderate densities of surface states are included. However, in a case with relatively high densities of surface states, the breakdown voltage could be drastically lowered when introducing a narrowly recessed gate structure. Effects of impact ionization on gate-lag phenomena in GaAs MESFETs are also studied. It is shown that the gate-lag becomes weaker when including the impact ionization. This is attributed to the fact that the potential profiles along the surface are drastically changed when the surface states capture generated carriers. It is suggested that there is a tradeoff relationship between raising the breakdown voltage and reducing the gate-lag.     

New heterostructure junction field-effect transistor (HJFET)

A new type of heterostructure junction field-effect transistor is proposed which is suitable for realisation in a heterojunction material combination such as AlGaAs-GaAs. The conducting region is a layer which is pinched off by the modulation of a unique n-n heterojunction, formed by either MOCVD or molecular-beam-epitaxial growth techniques. Threshold control is by ion implantation as in MOSFET technology.     

Improved charge control and frequency performance inInAs/AlSb-based heterostructure field-effect transistors

We demonstrate high-speed InAs/AlSb-based heterostructure field-effect transistors (HFET's) displaying greatly improved charge control properties and enhanced high-frequency gate performance. Microwave devices with a 0.5×84 μm² exhibit a peak unity current gain cut-off frequency of f_T=93 GHz. The HFET usable operational range was extended to V_DS=1.5 V (from V _DS=0.4-0.5 V) thus greatly enhancing the applicability of InAs/AlSb-based HFET's for low-power, high-frequency amplification. We also report on the bias dependence of f_T, and demonstrate that InAs/AlSb-based HFET's offer an attractive frequency performance over an adequately wide range of drain biases     

The impact of light on current DLTS and gate-lag transients of AlGaAs-GaAs HFETs

Gate-lag transients and "hole-like" deep level transient spectroscopy signals from AlGaAs-GaAs heterostructure field-effect transistors are shown to be suppressed by illumination with photons with energy larger than the AlGaAs bandgap. The observed pulse-response dependence on light intensity is reproduced and explained by two-dimensional numerical device simulations based on hole-trap behavior of surface deep levels.     

Deep level analysis in heterostructure field-effect transistors by means of the photo-FET method

The photo-FET method, a fast and simple room-temperature method for deep level analysis, was applied to heterostructure field-effect transistors for the first time. Well-known donor-like and several unknown acceptor-like levels were detected. By comparing heterostructures and homogeneously doped AlGaAs layers, GaAs- and AlGaAs-related traps could be separated. For comparison, similar samples were investigated independently by photocapacitance- and by low-frequency noise measurements. It was shown experimentally that superlattice buffers reduce the influence of GaAs related traps on the FET current. A simple model is proposed which relates the trap ionization in the AlGaAs to the carrier variation in the TEG.     

ANALYTICAL RESEARCH ON THE STATIC CHARACTERISTICS OF HETEROSTRUCTURE ISOLATED GATE FIELD-EFFECT TRANSISTORS

Based on improved charge control model and combining GSW velocity-field equa-tion, a series of analytical solutions for the static characteristics of HIGFETs such as I_D-V_D-V_G,I_(DS)-V_G, G_m and C_G are derived. The results of calculation are compared with experimentaldata reported in references, within the range of V_G<2V, I_D相似文献   

Incorporation of dielectric layers into the processing of III-nitride-based heterostructure field-effect transistors

Dielectric layers within III-nitride transistor technology can act either as passivation layers or as gate-dielectric layers. In this paper, we reflect on both issues and present novel approaches of dielectric schemes. In both cases, the elimination of surface traps or, more generally, of surface states is a key issue in obtaining improved device performance. As gate dielectrics, we introduced and investigated thermally and photoelectrochemically generated Al_xGa_2−xO₃, SiO₂, the combination of Al_xGa_2−xO₃ and SiO₂ (tandem-dielectric stack), and e-beam-deposited Al₂O₃. These dielectric layers serve simultaneously as a passivation layer. In addition, we introduced plasma-enhanced chemical-vapor deposition (PECVD)-deposited SiN_x for passivation. The results highlight the importance of passivation and the introduction of gate dielectrics and emphasize the relationship between surface states and improved direct-current (DC) performance. Backed by additional measurements, we proposed a different gateleakage mechanism for heterostructure field-effect transistor (HFET) and metal-oxide semiconductor heterostructure field-effect transistor (MOSHFET) devices.     

Flicker noise of GaN-based heterostructure field-effect transistors with Si-doped AlGaN carrier injection layer

Aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructure field effect transistors (HFETs) with and without Si-doped AlGaN layer were fabricated and investigated. HFETs with the Si-doped AlGaN carrier-injection layer show better DC performance, and the transconductance is 150 mS/mm. However, the HFETs with Si-doped AlGaN layer present the deviation from the 1/f noise at low frequency. The Lorentz shape was observed in the noise spectrum. It suggests that traps might be more pronounced in this kind of structure. Therefore, the DC characteristics of HFETs can be improved by the insertion of Si-doped AlGaN layer, but it can result in more low-frequency noise with the carrier-injection layer.     

Analysis of gate-lag phenomena in recessed-gate and buried-gateGaAs MESFETs

Two-dimensional analysis of gate-lag phenomena in recessed-gate and buried-gate GaAs MESFETs is performed, and their dependence on the structural parameters and the off-state gate voltage V_Goff is studied. It is shown that when V_Goff is around the threshold voltage (pinchoff voltage) V_th, the gate-lag could be almost eliminated by introducing the buried-gate structure. However, it is suggested that large gate-lag might be seen when V_Goff is much more negative than V_th     

Semiconductor-gated InGaAs/InAlAs heterostructure transistors (SISFET's)

We have successfully fabricated FET's with In0.53Ga0.47As channels, lattice-matched In0.52Al0.48As gate barriers, and n+ In0.53- Ga0.47As gates. For a barrier thickness of 600 Å and a gate length of 1.7 µm, the maximum transconductance is 250 mS/mm at T = 300 K. From gate capacitance measurements, the cutoff frequency is inferred to be ft= 15 GHz for this gate length. Self-aligned source and drain implants have been used to permit nonalloyed ohmic contacts with a characteristic resistance of 0.1 Ω.mm. The transconductance remains above 210 mS/mm for forward gate bias up to +1.0 V, confirming the usefulness of this gate structure for enhancement-mode devices.     

Influence of impact ionization on the drain conductance inInAs-AlSb quantum well heterostructure field-effect transistors

Using an InAs-AlSb heterostructure field-effect transistor (HFT) structure modified to incorporate an epitaxial p-type GaSb back gate, we measure the impact ionization current caused by hot electrons in the InAs channel. We show that the impact ionization current is only a small fraction of the deleterious increase in the drain current commonly observed in InAs-based transistors. Most of the drain current rise is caused by a feedback mechanism in which holes escaping into the substrate act like a positively charged parasitic back gate leading to an increase in the electron current flow in the channel by an amount that is large compared to the impact ionization current itself. Removal of the impact-generated holes by the epitaxial back gate breaks the feedback loop, and dramatically improves the DC characteristics of the devices, and increases the range of usable drain voltages     

Electrical characteristics of AlGaN/GaN metal-insulator semiconductor heterostructure field-effect transistors on sapphire substrates

The electrical performance of AlGaN/GaN metal-insulator semiconductor, heterostructure field-effect transistors (MISHFETs) were studied and compared to passivated and unpassivated HFETs. Record MISHFET current densities up to 1,010 mA/mm were achieved, and the devices exhibited stable operation at elevated temperatures up to 200°C. Higher maximum-drain current, breakdown voltage, and a lower gate-leakage current were obtained in the MISHFETs compared to unpassivated HFETs. The breakdown voltage of these devices exhibited a negative temperature coefficient of 0.14 VK⁻¹, suggesting that a mechanism other than impact ionization may be responsible. Different structures of MIS diodes also reveal that the high-field region at the gate edge dominates the breakdown mechanism of these devices. Gate-pulse measurements indicate the presence of current collapse in the MISHFETs, despite the expected passivation effect of the insulator. However, a striking feature observed was the mitigation of these effects upon annealing the devices at 385°C for 5 min under N₂ ambient.     

Modal analysis of IncGaAsP-InP,GaAs/AlGaAs-GaAs,and InGaAsP/AlGaAs-GaAs MIS heterostructure lasers

The transverse modal behavior of Metal-Insulator (Oxide)-Semiconductor (MIS) heterostructure injection lasers is analyzed. MIS structures have been proposed by Jain and Marciniec as an alternate approach to p-n heterojunctions to obtain minority carrier injection and subsequent lasing action. In the modal analysis the MIS structure is treated as an asymmetrical three-layer slab waveguide with appropriate boundary conditions. Numerical computations of electric field strength, intensity and confinement factor P are presented for various GaAs and InP based MIS structures. A comparison of the output characteristics of a GaAs MIS laser with a conventional GaAs p-n double heterostructure laser is also reported.     

Transient radiation effects in microwave monolithic integrated circuits based on heterostructure field-effect transistors: Experiment and model

The results of experimental studies and simulations of transient radiation effects in microwave monolithic integrated circuits, based on heterostructure field-effect transistors, affected by the pulse ionizing radiation, are presented. The physical model, which adequately describes transient radiation effects in field-effect transistors in dose rate range up to 10¹² rad/s, is proposed. Based on the physical model, the equivalent electric circuit, taking into account the dominating ionization effects, intended for using in the computer-aided design (CAD), is constructed. The simulated ionizing responses of the microwave low-noise amplifier (LNA) MIC are in accordance with the experimental data.     

Comparison for the carrier mobility between the III-V nitrides and AIGaAs/GaAs heterostructure field-effect transistors

Using the measured capacitance-voltage curves ofNi/Au Schottky contacts with different areas and the current-voltage characteristics for the A1GaAs/GaAs, A1GaN/A1N/GaN and InoAsA10.szN/A1N/GaN heterostructure field-effect transistors （HFETs） at low drain-source voltage, the two-dimensional electron gas （2DEG） electron mobility for the prepared HFETs was calculated and analyzed. It was found that there is an obvious difference for the variation trend of the mobility curves between the Ⅲ-V nitride HFETs and the A1GaAs/GaAs HFETs. In the III-V nitride HFETs, the variation trend for the curves of the 2DEG electron mobility with the gate bias is closely related to the ratio of the gate length to the drainto-source distance. While the ratio of the gate length to the drainto-source distance has no effect on the variation trend for the curves of the 2DEG electron mobility with the gate bias in the A1GaAs/GaAs HFETs. The reason is attributed to the polarization Coulomb field scattering in the Ⅲ-V nitride HFETs.     

Photoinduced negative magnetoresistance in 6,13-bis(triisopropylsilylethynyl)-pentacene field-effect transistors

We report on photoinduced negative organic magnetoresistance in low external magnetic-fields (<100 mT) in 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-Pentacene) field-effect transistors. An external magnetic field does not influence the dark current of our device. In contrast, there is a significant increase in photocurrent when magnetic field is applied to the irradiated device, which leads to negative magnetoresistance. The magnetoresistance and photoresponse values are strongly correlated and both are influenced by applied voltages and irradiation intensity. We attribute the observed photoinduced negative magnetoresistance in TIPS-Pentacene field-effect transistors to the presence of electron-hole pairs under irradiation. The overall dissociation probability of electron-hole pairs rises under the influence of an external magnetic field, which leads to a higher number of free charge carriers.