Investigation of AlGaN/GaN fluorine plasma treatment enhancement-mode high electronic mobility transistors by frequency-dependent capacitance and conductance analysis

This paper reports fluorine plasma treatment enhancement-mode HEMTs （high electronic mobility transistors） EHEMTs and conventional depletion-mode HEMTs DHEMTs fabricated on one wafer using separate litho-photography technology. It finds that fluorine plasma etches the AlGaN at a slow rate by capacitance-voltage measurement. Using capacitance-frequency measurement, it finds one type of trap in conventional DHEMTs with TT = （0.5 - 6） ms and DT ： （1 - 5）×10^13 cm^-2. eV^-1. Two types of trap are found in fluorine plasma treatment EHEMTs, fast with TW（f）= （0.2 - 2） μs and slow with TT（s） = （0.5 - 6） ms. The density of trap states evaluated on the EHEMTs is Dw（f） ： （1 - 3） × 10^12 cm^-2. eV^-1 and DT（s） =（2 - 6） × 10^12 cm-2. eV-1 for the fast and slow traps, respectively. The result shows that the fluorine plasma treatment reduces the slow trap density by about one order, but introduces a new type of fast trap. The slow trap is suggested to be a surface trap, related to the gate leakage current.

Enhancement-mode AlGaN/GaN high electronic mobility transistors with thin barrier

An enhancement-mode （E-mode） A1GaN/GaN high electron mobility transistor （HEMTs） was fabricated with 15-nm A1GaN barrier layer. E-mode operation was achieved by using fluorine plasma treatment and post-gate rapid thermal annealing. The thin barrier depletion-HEMTs with a threshold voltage typically around -1.7 V, which is higher than that of the 22-nm barrier depletion-mode HEMTs （-3.5 V）. Therefore, the thin barrier is emerging as an excellent candidate to realize the enhancement-mode operation. With 0.6-tim gate length, the devices treated by fluorine plasma for 150-W RF power at 150 s exhibited a threshold voltage of 1.3 V. The maximum drain current and maximum transconductance are 300 mA/mm, and 177 mS/ram, respectively. Compared with the 22-nm barrier E-mode devices, VT of the thin barrier HEMTs is much more stable under the gate step-stress,

Influence of optical phonons on the electronic mobility in a strained wurtzite AlN/GaN heterojunction under hydrostatic pressure

A variational method combined with solving the force balance equation is adopted to investigate the influence of strain and hydrostatic pressure on electronic mobility in a strained wurtzite AlN/GaN heterojunction by considering the scattering of optical-phonons in a temperature ranges from 250 to 600 K. The effects of conduction band bending and an interface barrier are also considered in our calculation. The results show that electronic mobility decreases with increasing hydrostatic pressure when the electronic density varies from 1.0 × 1012 to 6.5 × 1012 cm-2. The strain at the heterojunction interface also reduces the electronic mobility, whereas the pressure influence becomes weaker when strain is taken into account. The effect of strain and pressure becomes more obvious as temperature increases. The mobility first increases and then decreases significantly, whereas the strain and hydrostatic pressure reduce this trend as the electronic density increases at a given temperature （300 K）. The results also indicate that scattering from half space phonon modes in the channel side plays a dominant role in mobility.

Wearable Triboelectric Nanogenerators Based on Printed Polyvinylidene Fluoride Films Incorporated with Cobalt-Based Metal-Organic Framework for Self-Powered Mobile Electronics

In this study,wearable triboelectric nanogenerators comprising bar-printed polyvinylidene fluoride(PVDF)films incorporated with cobalt-based metal-organic framework(Co-MOF)were developed.The enhanced output performance of the TENGs was attributed to the phase transition of PVDF from a-crystals toβ-crystals,as facilitated by the incorporation of the MOF.The synthesis conditions,including metal ion,concentration,and particle size of the MOF,were optimized to increase open-circuit voltage(VOC)and open-circuit current(I_(SC))of PVDF-based TENGs.In addition to high operational stability,mechanical robustness,and long-term reliability,the developed TENG consisting of PVDF incorporated with Co-MOF(Co-MOF@PVDF)achieved a VOC of 194 V and an I_(SC)of 18.8μA.Furthermore,the feasibility of self-powered mobile electronics was demonstrated by integrating the developed wearable TENG with rectifier and control units to power a global positioning system(GPS)device.The local position of the user in real-time through GPS was displayed on a mobile interface,powered by the battery charged through friction-induced electricity generation.

Pressure effect on the electron mobility in AlAs/GaAs quantum wells

By taking the influence of optical phonon modes into account, this paper adopts the dielectric continuum phonon model and force balance equation to investigate the electronic mobility parallel to the interfaces for AlAs/GaAs semiconductor quantum wells （QWs） under hydrostatic pressure. The scattering from confined phonon modes, interface phonon modes and half-space phonon modes are analysed and the dominant scattering mechanisms in wide and narrow QWs are presented. The temperature dependence of the electronic mobility is also studied in the temperature range of optical phonon scattering being available. It is shown that the electronic mobility reduces obviously as pressure increases from 0 to 4GPa, the confined longitudinal optical （LO） phonon modes play an important role in wide QWs, whereas the interface optical phonon modes are dominant in narrow QWs, the half-space LO phonon modes hardly influence the electronic mobility expect for very narrow QWs.

MBE Growth of High Electron Mobility InP Epilayers

The molecular beam epitaxial growth of high quality epilayers on （100） InP substrate using a valve phosphorous cracker cell over a wide range of P/In BEP ratio （2.0-7.0） and growth rate （0.437 and 0. 791μm/h）. Experimental results show that electrical properties exhibit a pronounced dependence on growth parameters,which are growth rate, P/In BEP ratio, cracker zone temperature, and growth temperature. The parameters have been optimized carefully via the results of Hall measurements. For a typical sample, 77K electron mobility of 4.57 × 10^4 cm^2/（V · s） and electron concentration of 1.55×10^15 cm^-3 have been achieved with an epilayer thickness of 2.35μm at a growth temperature of 370℃ by using a cracking zone temperature of 850℃.

An Analytical Model of Electron Mobility for Strained-Si Channel nMOSFETs

An analytical model of electron mobility for strained-silicon channel nMOSFETs is proposed in this paper. The model deals directly with the strain tensor,and thus is independent of the manufacturing process. It is suitable for （100〉/ 〈110） channel nMOSFETs under biaxial or （100〉/〈 110 ） uniaxial stress and can be implemented in conventional device simulation tools .

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.

The real-time dynamic holographic display of LN:Bi,Mg crystals and defect-related electron mobility

Holographic display has attracted widespread interest because of its ability to show the complete information of the object and bring people an unprecedented sense of presence. The absence of ideal recording materials has hampered the realization of their commercial applications. Here we report that the response time of a bismuth and magnesium codoped lithium niobate(LN:Bi,Mg) crystal is shortened to 7.2 ms and a sensitivity as high as 646 cm/J. The crystal was used to demonstrate a real-time holographic display with a refresh rate of 60 Hz, as that of the popular high-definition television. Moreover, the first-principles calculations indicate that the electron mobility while Bi occupying Nb-site is significantly greater than that in Li-site, which directly induces the fast response of LN:Bi,Mg crystals when the concentration of Mg is above its doping threshold.

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.

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.

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.

Electron mobility anisotropy in (Al,Ga)Sb/InAs two-dimensional electron gases epitaxied on GaAs (001) substrates

The electron mobility anisotropy in (Al,Ga)Sb/InAs two-dimensional electron gases with different surface morphology has been investigated.Large electron mobility anisotropy is found for the sample with anisotropic morphology,which is mainly induced by the threading dislocations in the InAs layer.For the samples with isotropic morphology,the electron mobility is also anisotropic and could be attributed to the piezoelectric scattering.At low temperature (below transition temperature),the piezoelectric scattering is enhanced with the increase of temperature,leading to the increase of electron mobility anisotropy.At high temperature (above transition temperature),the phonon scattering becomes dominant.Because the phonon scattering is isotropic,the electron mobility anisotropy in all the samples would be reduced.Our results provide useful information for the comprehensive understanding of electron mobility anisotropy in the (Al,Ga)Sb/InAs system.

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.

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.

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.

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.

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.