Gate-drain Breakdown Voltage Research Articles

GaN microwave electronics

In this paper, recent progress of AlGaN/GaN-based power high-electron-mobility transistors (HEMT's) is reviewed. Remarkable improvement in performances was obtained through adoption of high Al contents in the AlGaN layer. The mobility in these modulation-doped structures is about 1200 cm/sup 2/.V/sup -1/.s/sup -1/ at 300 K with sheet densities of over 1/spl times/10/sup 13/ cm/sup -2/. The current density is over 1 A/mm with gate-drain breakdown voltages up to 280 V. F/sub t/ values up to 52 GHz have been demonstrated. Continuous wave (CW) power densities greater than 3 W/mm at 18 GHz have been achieved.

Enhanced breakdown voltage in InP-HEMTs by usingan In 0.53 (Al x Ga 1– x ) 0.47 As( x = 0.1, 0.2) quaternary channel

An In0.53(AlxGa1–x)0.47As quaternary channel has been introduced into n+-InAlAs/InGaAs HEMTs. By adding a small amount of Al to the InGaAs channel, the bandgap can be enhanced, which provides a higher reversed gate-drain breakdown voltage. In addition, the associated impact ionisation process can be suppressed in these quaternary channels. These HEMTs have been demonstrated with a very low output conductance (4 mS/mm for x = 0.2) and a much smaller gate leakage current than conventional InP-HEMTs.

A study of hot-electron degradation effects in pseudomorphic HEMTs

In this work we report on hot-electron stress experiments performed on commercial AlGaAs/InGaAs/GaAs pseudomorphic HEMTs. The stress cycles induce a permanent increase of the gate-drain breakdown voltage (breakdown walkout). Different characterization techniques are applied to thedevices under test, consistently indicating that the physical mechanism underlying walkout is the build-up of negative charge in the region between the gate and drain.

Bias dependent microwave performance of AlGaN/GaN MODFET's up to 100 V

1 /spl mu/m gate-length AlGaN/GaN modulation doped field effect transistors (MODFET's) have been fabricated on an insulating GaN buffer layer for better carrier confinement. These devices demonstrate simultaneously high current levels (>500 mA/mm), excellent pinch-off and high gate-drain breakdown voltages (220 V for 3 /spl mu/m gate-drain spacing). In contrast to their GaAs counterparts, the current-gain cutoff frequency of the AlGaN/GaN devices shows little degradation at high drain voltage biases. A power-gain cutoff frequency of 19 GHz is obtained at 100 V. ACW power density of 1.57 W/mm at 4 Ghz is also achieved when biased at 28 V and 205 mA/mm.

Ga/sub 0.51/In/sub 0.49/P/In/sub 0.15/Ga/sub 0.85/As/GaAs pseudomorphic doped-channel FET with high-current density and high-breakdown voltage

Ga/sub 0.51/In/sub 0.49/P/In/sub 0.15/Ga/sub 0.85/As/GaAs pseudomorphic doped-channel FETs exhibiting excellent DC and microwave characteristics were successfully fabricated. A high peak transconductance of 350 mS/mm, a high gate-drain breakdown voltage of 31 V and a high maximum current density (575 mA/mm) were achieved. These results demonstrate that high transconductance and high breakdown voltage could be attained by using In/sub 0.15/Ga/sub 0.85/As and Ga/sub 0.51/In/sub 0.49/P as the channel and insulator materials, respectively. We also measured a high-current gain cut-off frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> of 23.3 GHz and a high maximum oscillation frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 50.8 GHz for a 1-μm gate length device at 300 K. RF values where higher than those of other works of InGaAs channel pseudomorphic doped-channel FETs (DCFETs), high electron mobility transistors (HEMTs), and heterostructure FETs (HFETs) with the same gate length and were mainly attributed to higher transconductance due to higher mobility, while the DC values were comparable with the other works. The above results suggested that Ga/sub 0.51/In/sub 0.49/P/In/sub 0.15/Ga/sub 0.85/As/GaAs doped channel FET's were were very suitable for microwave high power device application.

Improved breakdown voltages in submicrometre planarGaAs MESFETs with a thin (Ga,In)P surface layer

A thin 100 Å (Ga,In)P surface layer in the extrinsic gate-to-drain space of the transistor improves the power-handling capabilities of MOCVD-grown planar GaAs MESFETs. The authors demonstrate 0.8 µm devices with drain and gate-drain breakdown voltages of 21 and 23–24 V, respectively. Although achieved in non-optimised structures, the results are comparable to some obtained with more complicated passivation approaches.

Very high current density pseudomorphic double channelIn 0.49 Ga 0.51 P/In 0.3 Ga 0.7 As/GaAs HEMT

The authors report the results of a 0.7 µm gate-length pseudomorphic double channel In0.49Ga0.51P/In0.3Ga0.7As/GaAs HEMT for communication systems applications. The devices achieved a very high saturation current density of 801 mA/mm and a maximum peak transconductance of 256 mS/mm. The maximum gate-drain breakdown voltage measured was –7.8 V.

4H-SiC MESFET's with 42 GHz f/sub max/

We report for the first time the development of state-of-the-art SiC MESFETs on high-resistivity 4H-SiC substrates. 0.5 /spl mu/m gate MESFETs in this material show a new record high f/sub max/ of 42 GHz and RF gain of 5.1 dB at 20 GHz. These devices also show simultaneously high drain current, and gate-drain breakdown voltage of 500 mA/mm, and 100 V, respectively showing their potential for RF power applications.

Breakdown walkout in pseudomorphic HEMT's

In this work we show for the first time evidence of gate-drain breakdown walkout due to hot electrons in pseudomorphic AlGaAs-InGaAs-GaAs HEMTs (PHEMTs). Experiments performed on passivated commercial PHEMTs show that hot electron stress cycles induce a large and permanent increase of the gate-drain breakdown voltage. Three-terminal and two-terminal stress conditions are compared, the former producing a much larger walkout due to hot electrons flowing in the channel. Experimental results indicate that a build-up of negative charge in the region between gate and drain is responsible for the breakdown walkout, due to a local widening of the depletion region and a reduction of the peak electric field.

Growth of High Quality (In,Ga,Al)N/GaN Heterostructure Materials and Devices by Atmospheric Pressure MOCVD

AbstractUsing atmospheric pressure MOCVD we have obtained high quality InGaN/GaN and AlGaN/GaN heterostructure materials and devices. For nominally undoped 4 μm thick GaN films, we obtained 300 K mobilities of 780 cm2/Vs and an unintentional background impurity level of n300K = 6*1016 cm−3. For InGaN/GaN heterostructures we have obtained direct band-edge transitions with FWHM as narrow as 7.9 nm (59 meV) for 50Å thick In0.16Ga0.84N quantum wells at 300K, which is the among the best reported values. The quantum wells display energy shifts towards shorter wavelength with decreasing well thickness, and the shift agrees with predicted quantum effects. These materials have been incorporated into InGaN single quantum well LEDs that emit at 450 nm. In addition AlGaN/GaN heterostructure materials have been incorporated into HFETs and MODFETs. Gate-drain breakdown voltage well exceeding 100 V, and extrinsic transconductance gm of up to 140 mS/mm were realized in the MODFET.

Enhancement-mode buried gate InGaP/AlGaAs/InGaAsheterojunction FETs fabricated by selective wet etching

Enhancement-mode buried gate InGaP/AlGaAs/InGaAs heterojunction FETs (HJFETs) were successfully fabricated by using a highly-selective wet recess etching technique. The fabricated HJFET exhibited a maximum drain current of 202 mA/nm, a peak transconductance of 330 mS/mm and a gate-drain breakdown voltage of 33 V. Standard deviation of the threshold voltage was 60 mV, which is less than one fifth that of the conventional AlGaAs/InGaAs HJFET. No appreciable frequency dispersion in the drain current was measured, indicating that the developed InGaP/AlGaAs/InGaAs HJFET with a buried gate structure is promising for large-signal microwave power applications.

Two step doping channel FET with symmetric normally on and normally off characteristics

An n −- GaAs n +- InGaAs two step doping channel FET prepared by MOCVD has been built for large input signals circuit applications. The thin InGaAs channel was heavily doped to increase current carrier density, resulting in a maximum current density of 930 mA/mm, and to improve the transconductance linearity, giving a very broad gate voltage range from 2.2 to −2.0 V. On the other hand, thick and lightly doped GaAs channel layer works as carrier confinement to reduce the gate leakage current and to enhance the breakdown voltage. A device with 2 × 100 μm 2 has yielded a maximum extrinsic transconductance of 230 mS/mm, a general gate-drain breakdown voltage of > 17 V and a f t = 15 GHz × μm. The performance of this device shows that two step doping channel FETs are very promising for high speed, high power and large input signal analog circuit applications.

High-breakdown AlGaAs/InGaAs/GaAs PHEMT with telluriumdoping

The authors report the fabrication and characterisation of an Al0.43Ga0.57As/In0.2Ga0.8As/GaAs pseudomorphic HEMT (PHEMT) with high channel conductivity grown by solid source MBE. The high conductivity of the channel is a direct consequence of the high sheet charge and high mobility that has recently been obtained by using tellurium as the n-type dopant in 43% AlGaAs. The device characteristics reflect the resulting reduction in the parasitic resistances of the high channel conductivity. Microwave measurements yield a short-circuit current gain cutoff frequency fT of 11 GHz and maximum oscillation frequency fmax of 25 GHz. A high gate-drain breakdown voltage of 26 V along with a maximum drain current density of 400 mA/mm obtained in the device illustrate the applicability of this technology in microwave power field effect transistors.

New high power planar gate GaAs MESFETswith improved gate-drain breakdown voltage

The authors present a new approach to power GaAs MESFETs with planar gate structures, based on the MBE growth technique on an undoped surface GaAs layer on an ion-implanted channel layer. This undoped GaAs layer increases the gate-drain breakdown voltage and serves as both an ideal passivation layer and an ideal annealing cap of ion implanted channels. To realise a good surface condition before MBE growth, the UV-ozone surface treatment is introduced. This new simple structure offers high performance power GaAs MESFETs.

(Al/sub 0.7/Ga/sub 0.3/)/sub 0.5/In/sub 0.5/P/In/sub 0.15/Ga/sub 0.85/As/Ga As heterostructure field effect transistors with very thin highly p-doped surface layer

(Al/sub 0.7/Ga/sub 0.3/)/sub 0.5/In/sub 0.5/P/In/sub 0.15/Ga/sub 0.85/As/Ga As Heterostructure Field Effect Transistors (HFETs) were realized for the first time using low pressure metal organic chemical vapor deposition on GaAs substrates. Maximum extrinsic transconductance and saturation current of g/sub m/=368 mS/mm and I/sub DS/=326 mA/mm were measured, respectively, for a device with a gate length of L/sub G/=0.35 /spl mu/m. Although using self-aligned ohmic contacts, the devices showed very small output conductance of g/sub d//spl les/10 mS/mm and high gate-drain breakdown voltage of V/sub BrGD/=19 V. The cut-off frequencies were determined to be f/sub T/=52 GHz and f/sub max/=120 GHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Breakdown Mechanisms in Pseudomorphic InAlAs/InxGa1-xAs High Electron Mobility Transistors on InP. I: Off-State

A systematic experimental study on the mechanisms which are inducing device breakdown in the off-state in L G=0.28 µ m gate-length pseudomorphic InAlAs/Inx Ga1-x As (0.53< x<0.7) High Electron Mobility Transistors on InP substrate is presented. The study identifies the present limitations of this type of device made with this material system. The investigation encompasses temperature- and mole fractional dependent two-terminal and three-terminal dc-measurements. The results of the investigation clarify that breakdown is a combined process of thermionic field emission and impact ionization. Up to high drain bias, thermionic field emission is the dominant process, only at very high drain bias impact ionization occurs. The experimental results also indicate that off-state breakdown is surface related. The drain-source breakdown voltages were determined to be V BRDS=8 V, 5.9 V, 5.2 V, 4.3 V, 2.5 V for x=0.53, 0.59, 0.62, 0.65 and x=0.7, respectively. The two-terminal gate-drain breakdown voltages at room-temperature were determined to be V BRGD=11.9 V, 11.3 V, 7.9 V, 7.2 V, 6.7 V for x=0.53, 0.59, 0.62, 0.65 and x=0.7, respectively.

0.2 µm AlSb/InAs HEMTs with 5 V gate breakdownvoltage

DC and microwave measurements on AlSb/InAs HEMTs with a gate length of 0.21 mu m are reported. The reverse gate characteristics exhibit relatively low gate leakage current and gate-drain breakdown voltages as high as 5 V. Equivalent circuit modelling yields an f/sub T/ of 110 GHz after removal of the gate bonding pad capacitance. The bias dependence of f/sub max/ is examined indicating a significant reduction in the unilateral gain due to impact ionisation.

Reactive ion etching-induced damage in InAlAs/InGaAs heterostructure field-effect transistors processed in HBr plasma

An investigation of the effects of HBr reactive ion etching (RIE) processing for gate recessing in lattice-matched InAlAs/InGaAs heterostructure field-effect transistors (HFETs) has been conducted. The effect of varying the Schottky barrier layer thickness on device performance and the susceptibility of HFETs to RIE-induced damage are presented for barrier layer thicknesses ranging from 10 to 25 nm. The effect of plasma self-bias voltage during gate recess etching on overall device performance for a given layer structure is also examined for voltages ranging from −100 to −200 V. Device performance is assessed through direct current (dc) characterization of transconductance, threshold voltage, reverse gate leakage current, and gate-drain breakdown voltage, and through microwave characterization of the devices. Devices with barrier layers less than 20 nm thick are found to suffer the most degradation due to RIE-induced damage. For devices with sufficiently thick barrier layers, dc and microwave device parameters compare well with those of corresponding devices fabricated using a selective wet-etch process.

Realisation of doped-channel MISFETs with highbreakdown voltage in AlGaAs/InGaAs based materialsystem

The authors report the realisation of a doped-channel MISFET with high drain-source and gate-drain breakdown voltages of 41 and -37 V, respectively, and a record low output conductance of 150 mu S/mm. These characteristics are achieved through the use of n-type highly doped In/sub 0.26/Ga/sub 0.74/As as the channel material and a short period (AlAs)/sub 3/(GaAs)/sub 4/ superlattice as the gate insulator and the lower barrier grown on GaAs

High performance InP JFETs grown by MOCVD using tertiarybutylphosphine

Indium phosphide channel junction field effect transistors were fabricated by metalorganic chemical vapor deposition using tertiarybulylphosphine (TBP) as the alternative source for phosphine. At growth temperatures of 600°C, InP with specular surface morphology and mobilities as high as 61000 cm2/V s at 77Khas been achieved using trimethylindium and TBP. To improve device isolation, pinch-off characteristics, and output transconductance, we employ a high resistivity (1 × 108 Ω-cm) semi-insulating InP buffer layer using ferrocene as the Fe-dopant. Devices with gate lengths of 1 urn exhibit very high extrinsic transconductance of 130 mS/mm, gate-drain breakdown voltage exceeding 20 V, maximum current density of >450 mA/mm with record high fT and fmax of 15 GHz and 35 GHz, respectively. These results indicate: that InP JFETs are promising electronic devices for microwave power amplification, and that TBP is capable of device quality materials.