Degraded model of radiation-induced acceptor defects for GaN-based high electron mobility transistors(HEMTs)

Using depletion approximation theory and introducing acceptor defects which can characterize radiation induced deep-level defects in AlGaN/GaN heterostructures,we set up a radiation damage model of AlGaN/GaN high electron mobility transistor （HEMT） to separately simulate the effects of several main radiation damage mechanisms and the complete radiation damage effect simultaneously considering the degradation in mobility. Our calculated results,consistent with the experimental results,indicate that thin AlGaN barrier layer,high Al content and high doping concentration are favourable for restraining the shifts of threshold voltage in the AlGaN/GaN HEMT;when the acceptor concentration induced is less than 10^14cm-3,the shifts in threshold voltage are not obvious;only when the acceptor concentration induced is higher than 10^16cm-3,will the shifts of threshold voltage remarkably increase;the increase of threshold voltage,resulting from radiation induced acceptor,mainly contributes to the degradation in drain saturation current of the current-voltage （Ⅰ-Ⅴ） characteristic,but has no effect on the transconductance in the saturation area.

A bistable, self-latching inverter by the monolithic integration of resonant tunnelling diode and high electron mobility transistor

This paper reports that the structures of AlGaAs/InGaAs high electron mobility transistor （HEMT） and AlAs/GaAs resonant tunnelling diode （RTD） are epitaxially grown by molecular beam epitaxy （MBE） in turn on a GaAs substrate. An Alo.24Gao.76As chair barrier layer, which is grown adjacent to the top AlAs barrier, helps to reduce the valley current of RTD. The peak-to-valley current ratio of fabricated RTD is 4.8 and the transconductance for the 1-μm gate HEMT is 125mS/mm. A static inverter which consists of two RTDs and a HEMT is designed and fabricated. Unlike a conventional CMOS inverter, the novel inverter exhibits self-latching property.

Monolithic Integration of GaAs-Based Resonant Tunneling Diode and High Electron Mobility Transistor

The resonant tunneling diode (RTD) is a kind of novel ultra-high speed and ultra-high frequency negative differential resistance nanoelectronic device. Integration of RTD and other three-terminal compound semiconductor devices is one important direction of high speed integrated circuit development. In this paper, monolithic integration technology of RTD and high electron mobility transistor (HEMT) based on GaAs substrate was discussed. A top-RTD and bottom-HEMT material structure was proposed and epitaxyed. Based on wet chemical etching, electron beam lithography, metal lift-off and air bridge technology, RTD and HEMT were fabricated on the same wafer. The peak-to-valley current ratio of RTD is 4 and the peak voltage is 0.5 V. The maximal transconductance is 120 mS/mm for a 0.25 μm gate length depletion mode HEMT. Current levels of two devices are basically suited. The results validate the feasibility of the designed integration process.

Device Characteristics Comparison Between GaAs Single and Double Delta-Doped Pseudomorphic High Electron Mobility Transistors

The Al 0.24Ga 0.76As/In 0.22Ga 0.78As single delta-doped PHEMT (SH-PHEMT) and double delta-doped PHEMT (DH-PHEMT) are fabricated and investigated.Based on the employment of double heterojunction,double delta doped design,the DH-PHEMT can enhance the carrier confinement,increase the electron gas density,and improve the electron gas distribution,which is beneficial to the device performance.A high device linearity,high transconductance over a large gate voltage swing,high current drivability are found in DH-PHEMT.These improvements suggest that DH-PHEMT is more suitable for high linearity applications in microwave power device.

Evaluation of thermal resistance constitution for packaged AlGaN/GaN high electron mobility transistors by structure function method

The evaluation of thermal resistance constitution for packaged A1GaN/GaN high electron mobility transistor （HEMT） by structure function method is proposed in this paper. The evaluation is based on the transient heating measurement of the A1GaN/GaN HEMT by pulsed electrical temperature sensitive parameter method. The extracted chip-level and package-level thermal resistances of the packaged multi-finger A1GaN/GaN HEMT with 400μm SiC substrate are 22.5 K/W and 7.2 K/W respectively, which provides a non-invasive method to evaluate the chip-level thermal resistance of packaged A1GaN/GaN HEMTs. It is also experimentally proved that the extraction of the chip- level thermal resistance by this proposed method is not influenced by package form of the tested device and temperature boundary condition of measurement stage.

Enhancement of terahertz coupling efficiency by improved antenna design in GaN/AlGaN high electron mobility transistor detectors

An optimized micro-gated terahertz detector with novel triple resonant antenna is presented.The novel resonant antenna operates at room temperature and shows more than a 700% increase in photocurrent response compared to the conventional bowtie antenna.In finite-difference-time-domain simulations,we found the performance of the self-mixing GaN/AlGaN high electron mobility transistor detector is mainly dependent on the parameters L gs（the gap between the gate and the source/drain antenna） and L w（the gap between the source and drain antenna）.With the improved triple resonant antenna,an optimized micrometer-sized AlGaN/GaN high electron mobility transistor detector can achieve a high responsivity of 9.45×102 V/W at a frequency of 903 GHz at room temperature.

Two-dimensional electron gas characteristics of InP-based high electron mobility transistor terahertz detector

The samples of InxGa（1-x）As/In（0.52）Al（0.48）As two-dimensional electron gas（2DEG）are grown by molecular beam epitaxy（MBE）.In the sample preparation process,the In content and spacer layer thickness are changed and two kinds of methods,i.e.,contrast body doping andδ-doping are used.The samples are analyzed by the Hall measurements at 300 Kand 77 K.The InxGa1-xAs/In0.52Al0.48As 2DEG channel structures with mobilities as high as 10289 cm^2/V·s（300 K）and42040 cm^2/V·s（77 K）are obtained,and the values of carrier concentration（Nc）are 3.465×10^12/cm^2 and 2.502×10^12/cm^2,respectively.The THz response rates of In P-based high electron mobility transistor（HEMT）structures with different gate lengths at 300 K and 77 K temperatures are calculated based on the shallow water wave instability theory.The results provide a reference for the research and preparation of In P-based HEMT THz detectors.

High-electric-field-stress-induced degradation of SiN passivated AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors （HEMTs） are fabricated by employing SiN passivation, this paper investigates the degradation due to the high-electric-field stress. After the stress, a recoverable degradation has been found, consisting of the decrease of saturation drain current IDsat, maximal transconductance gm, and the positive shift of threshold voltage VTH at high drain-source voltage VDS. The high-electric-field stress degrades the electric characteristics of AlGaN/GaN HEMTs because the high field increases the electron trapping at the surface and in AlGaN barrier layer. The SiN passivation of AlGaN/GaN HEMTs decreases the surface trapping and 2DEC depletion a little during the high-electric-field stress. After the hot carrier stress with VDS = 20 V and VGS= 0 V applied to the device for 104 sec, the SiN passivation decreases the stress-induced degradation of IDsat from 36% to 30%. Both on-state and pulse-state stresses produce comparative decrease of IDsat, which shows that although the passivation is effective in suppressing electron trapping in surface states, it does not protect the device from high-electric-field degradation in nature. So passivation in conjunction with other technological solutions like cap layer, prepassivation surface treatments, or field-plate gate to weaken high-electric-field degradation should be adopted.

Novel model of a AlGaN/GaN high electron mobility transistor based on an artificial neural network

In this paper we present a novel approach to modeling AlGaN/GaN high electron mobility transistor （HEMT） with an artificial neural network （ANN）. The AlGaN/GaN HEMT device structure and its fabrication process are described. The circuit-based Neuro-space mapping （neuro-SM） technique is studied in detail. The EEHEMT model is implemented according to the measurement results of the designed device, which serves as a coarse model. An ANN is proposed to model AIGaN/CaN HEMT based on the coarse model. Its optimization is performed. The simulation results from the model are compared with the measurement results. It is shown that the simulation results obtained from the ANN model of A1GaN/GaN HEMT are more accurate than those obtained from the EEHEMT model.

Influence of a drain field plate on the forward blocking characteristics of an AlGaN/GaN high electron mobility transistor

In this paper, the influence of a drain field plate （FP） on the forward blocking characteristics of an AlGaN/GaN high electron mobility transistor （HEMT） is investigated. The HEMT with only a gate FP is optimized, and breakdown voltage VBR is saturated at 1085 V for gate–drain spacing LGD ≥ 8 μm. On the basis of the HEMT with a gate FP, a drain FP is added with LGD=10 μm. For the length of the drain FP LDF ≤ 2 μm, VBR is almost kept at 1085 V, showing no degradation. When LDF exceeds 2 μm, VBR decreases obviously as LDF increases. Moreover, the larger the LDF, the larger the decrease of VBR. It is concluded that the distance between the gate edge and the drain FP edge should be larger than a certain value to prevent the drain FP from affecting the forward blocking voltage and the value should be equal to the LGD at which VBR begins to saturate in the first structure. The electric field and potential distribution are simulated and analyzed to account for the decrease of VBR.

Effect of defects properties on InP-based high electron mobility transistors

The performance damage mechanism of InP-based high electron mobility transistors(HEMTs) after proton irradiation has been investigated comprehensively through induced defects.The effects of the defect type, defect energy level with respect to conduction band ET, and defect concentration on the transfer and output characteristics of the device are discussed based on hydrodynamic model and Shockley–Read–Hall recombination model.The results indicate that only acceptorlike defects have a significant influence on device operation.Meanwhile, as defect energy level ETshifts away from conduction band, the drain current decreases gradually and finally reaches a saturation value with ETabove 0.5 eV.This can be attributed to the fact that at sufficient deep level, acceptor-type defects could not be ionized any more.Additionally,the drain current and transconductance degrade more severely with larger acceptor concentration.These changes of the electrical characteristics with proton radiation could be accounted for by the electron density reduction in the channel region from induced acceptor-like defects.

High performance InAlN/GaN high electron mobility transistors for low voltage applications

A high performance InAlN/GaN high electron mobility transistor(HEMT)at low voltage operation(6-10 V drain voltage)has been fabricated.An 8 nm InAlN barrier layer is adopted to generate large 2DEG density thus to reduce sheet resistance.Highly scaled lateral dimension(1.2μm source-drain spacing)is to reduce access resistance.Both low sheet resistance of the InAlN/GaN structure and scaled lateral dimension contribute to an high extrinsic transconductance of 550 mS/mm and a large drain current of 2.3 A/mm with low on-resistance(Ron)of 0.9Ω·mm.Small signal measurement shows an fT/fmax of 131 GHz/196 GHz.Large signal measurement shows that the InAlN/GaN HEMT can yield 64.7%-52.7%(Vds=6-10 V)power added efficiency(PAE)associated with 1.6-2.4 W/mm output power density at 8 GHz.These results demonstrate that GaN-based HEMTs not only have advantages in the existing high voltage power and high frequency rf field,but also are attractive for low voltage mobile compatible rf applications.

Characteristics of AlGaN/GaN high electron mobility transistors on metallic substrate

We have successfully prepared GaN based high electron mobility transistors(HEMTs)on metallic substrates transferred from silicon substrates by electroplating technique.GaN HEMTs on Cu substrates are demonstrated to basically have the same good electric characteristics as the chips on Si substrates.Furthermore,the better heat dissipation of HEMTs on Cu substrates compared to HEMTs on Si substrates is clearly observed by thermoreflectance imaging,showing the promising potential for very high-power and high-temperature operation.This work shows the outstanding ability of HEMT chips on Cu substrates for solving the self-heating effect with the advantages of process simplicity,high yield,and low production requirement.

Breakdown voltage analysis of Al_(0.25)Ga_(0.75)N/GaN high electron mobility transistors with partial silicon doping in the AlGaN layer

In this paper,two-dimensional electron gas（2DEG） regions in AlGaN/GaN high electron mobility transistors（HEMTs） are realized by doping partial silicon into the AlGaN layer for the first time.A new electric field peak is introduced along the interface between the AlGaN and GaN buffer by the electric field modulation effect due to partial silicon positive charge.The high electric field near the gate for the complete silicon doping structure is effectively decreased,which makes the surface electric field uniform.The high electric field peak near the drain results from the potential difference between the surface and the depletion regions.Simulated breakdown curves that are the same as the test results are obtained for the first time by introducing an acceptor-like trap into the N-type GaN buffer.The proposed structure with partial silicon doping is better than the structure with complete silicon doping and conventional structures with the electric field plate near the drain.The breakdown voltage is improved from 296 V for the conventional structure to 400 V for the proposed one resulting from the uniform surface electric field.

Influence of a two-dimensional electron gas on current-voltage characteristics of Al_(0.3)Ga_(0.7) N/GaN high electron mobility transistors

The J-V characteristics of AltGa1 tN/GaN high electron mobility transistors（HEMTs） are investigated and simulated using the self-consistent solution of the Schro dinger and Poisson equations for a two-dimensional electron gas（2DEG） in a triangular potential well with the Al mole fraction t = 0.3 as an example.Using a simple analytical model,the electronic drift velocity in a 2DEG channel is obtained.It is found that the current density through the 2DEG channel is on the order of 10^13 A/m^2 within a very narrow region（about 5 nm）.For a current density of 7 × 10^13 A/m62 passing through the 2DEG channel with a 2DEG density of above 1.2 × 10^17 m^-2 under a drain voltage Vds = 1.5 V at room temperature,the barrier thickness Lb should be more than 10 nm and the gate bias must be higher than 2 V.

Kink effect in AlGaN/GaN high electron mobility transistors by electrical stress

The kink effect is studied in an AlGaN/GaN high electron mobility transistor by measuring DC performance during fresh, short-term stress and recovery cycle with negligible degradation. Vdg plays an assistant role in detrapping electrons and short-term stress results in no creation of new category traps but an increase in number of active traps. A possible mechanism is proposed that electrical stress supplies traps with the electric field for activation and when device is under test field-assisted hot-electrons result in electrons detrapping from traps, thus deteriorating the kink effect. In addition, experiments show that the impact ionization is at a relatively low level, which is not the dominant mechanism compared with trapping effect. We analyse the complicated link between the kink effect and stress bias through groups of electrical stress states： Pals = 0-state, off-state, on-state （on-state with low voltage, high-power state, high field state）. Finlly, a conclusion is drawn that electric field brings about more severe kink effect than hot electrons. With the assistance of electric field, hot electrons tend to be possible to modulate the charges in deep-level trap.

High temperature characteristics of AlGaN/GaN high electron mobility transistors

Direct current （DC） and pulsed measurements are performed to determine the degradation mechanisms of A1GaN/GaN high electron mobility transistors （HEMTs） under high temperature. The degradation of the DC characteristics is mainly attributed to the reduction in the density and the mobility of the two-dimensional electron gas （2DEG）. The pulsed measurements indicate that the trap assisted tunneling is the dominant gate leakage mechanism in the temperature range of interest. The traps in the barrier layer become active as the temperature increases, which is conducive to the electron tunneling between the gate and the channel. The enhancement of the tunneling results in the weakening of the current collapse effects, as the electrons trapped by the barrier traps can escape more easily at the higher temperature.

Neutron irradiation effects on AlGaN/GaN high electron mobility transistors

A1GaN/GaN high electron mobility transistors （HEMTs） were exposed to 1 MeV neutron irradiation at a neutron ftuence of 1 × 10^15 cm-2. The dc characteristics of the devices, such as the drain saturation current and the maximum transconductance, decreased after neutron irradiation. The gate leakage currents increased obviously after neutron irradiation. However, the rf characteristics, such as the cut-off frequency and the maximum frequency, were hardly affected by neutron irradiation. The A1GaN/GaN heterojunctions have been employed for the better understanding of the degradation mechanism. It is shown in the Hall measurements and capacitance voltage tests that the mobility and concentration of two-dimensional electron gas （2DEG） decreased after neutron irradiation. Tbere was no evidence of the full-width at half-maximum of X-ray diffraction （XRD） rocking curve changing after irradiation, so the dislocation was not influenced by neutron irradiation. It is concluded that the point defects induced in A1GaN and GaN by neutron irradiation are the dominant mechanisms responsible for performance degradations of A1GaN/GaN HEMT devices.

Effects of Si δ-Doping Condition and Growth Interruption on Electrical Properties of InP-Based High Electron Mobility Transistor Structures

The InGaAs/InAIAs/InP high electron mobility transistor （HEM：F） structures with lattice-matched and pseudo- morphic channels are grown by gas source molecular beam epitaxy. Effects of Si ^-doping condition and growth interruption on the electrical properties are investigated by changing the Si-cell temperature, doping time and growth process. It is found that the optimal Si ^-doping concentration （Nd） is about 5.0 x 1012 cm-2 and the use of growth interruption has a dramatic effect on the improvement of electrical properties. The material structure and crystal interface are analyzed by secondary ion mass spectroscopy and high resolution transmission elec- tron microscopy. An InGaAs/InAiAs/InP HEMT device with a gate length of lOOnm is fabricated. The device presents good pinch-off characteristics and the kink-effect of the device is trifling. In addition, the device exhibits fT = 249 GHa and fmax 〉 400 GHz.

Enhancement of Breakdown Voltage in AlGaN/GaN High Electron Mobility Transistors Using Double Buried p-Type Layers

A novel A1GaN/GaN high electron mobility transistor （HEMT） with double buried p-type layers （DBPLs） in the GaN buffer layer and its mechanism are studied. The DBPL A1GaN/GaN HEMT is characterized by two equi-long p-type GaN layers which are buried in the GaN buffer layer under the source side. Under the condition of high-voltage blocking state, two reverse p-n junctions introduced by the buried p-type layers will effectively modulate the surface and bulk electric fields. Meanwhile, the buffer leakage is well suppressed in this structure and both lead to a high breakdown voltage. The simulations show that the breakdown voltage of the DBPL structure can reach above 2000 V from 467 V of the conventional structure with the same gate-drain length of 8μm.