Performance of AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistors with AlN gate insulator prepared by reactive magnetron sputtering
TL;DR: In this article, the reactive magnetron sputtering technique at room temperature was used to prepare AlN dielectric layer for application in AlGaN/GaN metal-insulator-semiconductor heterostructure field effect transistors (MIS-HFETs).
Abstract: The reactive magnetron sputtering technique at room temperature was used to prepare AlN dielectric layer for application in AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs). Two different gas ambiences (mixture of nitrogen and argon N2/Ar=0.35 and N2 alone, respectively) were applied. An increase in the saturation drain current (∼50%) and transconductance (∼45%) of the MIS-HFETs compared with HFET counterparts (IDS=363 mA/mm and gm=114 mS/mm) was observed. AlN/AlGaN/GaN MIS-HFET, where only the nitrogen gas ambience was used to deposit an AlN dielectric layer, reduced the gate leakage current up to four orders of magnitude (∼10−8 A/mm at −5 V) in comparison with the HFET. The improvements of the dynamic characteristics of the MIS-HFETs (reduction of the current collapse and density of the slow traps) were achieved. The N2 MIS-HFET exhibits better improvements of the static and dynamic parameters than the ArN2 MIS-HFET, and therefore the deposition of the AlN lay...
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TL;DR: In this article, the capacitance-frequency-temperature (C-f-T) mapping was used to obtain the activation energies of electron trapping, namely the interface state energy levels, for a wide range of the gate biases.
Abstract: AlN/AlGaN/GaN metal-insulator-semiconductor (MIS) structure is analyzed by using capacitance-frequency-temperature (C-f-T) mapping. Applying sputtering-deposited AlN, we attained AlN/AlGaN/GaN MIS heterostructure field-effect transistors with much suppressed gate leakage currents, but exhibiting frequency dispersion in C-V characteristics owing to high-density AlN/AlGaN interface states. In order to investigate the interface states deteriorating the device performance, we measured temperature-dependent frequency dispersion in the C-V characteristics. As a result, we obtained C-f-T mapping, whose analysis gives the activation energies of electron trapping, namely the interface state energy levels, for a wide range of the gate biases. This analysis method is auxiliary to the conventional conductance method, serving as a valuable tool for characterization of wide-bandgap devices with deep interface states. From the analysis, we can directly evaluate the gate-control efficiency of the devices.
38 citations
TL;DR: In this paper, an exact exponential dependence of AlGaN/GaN hetero-interface trap time constants with gate bias was observed in the vicinity of threshold voltage, and the high resolution x-ray rocking curve and Van der Pauw-Hall measurements also confirmed that increasing the buffer thickness improved the performance of the HEMT heterostructures with reduced edge dislocation densities.
Abstract: We report on the analyses of trapping properties of metal-organic chemical vapor deposition grown AlGaN/GaN high-electron-mobility transistor (HEMT) heterostructures on silicon with increasing buffer thickness (Tbuff). An exact exponential dependence of AlGaN/GaN hetero-interface trap time constants with gate bias was observed in the vicinity of threshold voltage. A low hetero-interface state density (Dit) value of ∼2.5 × 1010 cm−2 eV−1 was achieved for heterostructures grown by using thick Tbuff ∼ 5 μm against a Dit value of ∼1 × 1011 cm−2 eV−1 for a similar heterostructures grown with thin Tbuff ∼ 1.25 μm. Further, the high resolution x-ray rocking curve and Van der Pauw-Hall measurements also confirmed that increasing the Tbuff improves the AlGaN/GaN HEMT heterostructures with reduced edge dislocation densities and enhanced carrier transport properties.
20 citations
TL;DR: In this paper, an underlap double gate (U-DG) Symmetric Heterojunction AlGaN/GaN Metal Oxide Semiconductor High Electron Mobility Transistor (MOS-HEMT) with gate oxide materials of different dielectric constant has been studied using gate oxide material such as Hafnium dioxide (HfO2), Silicon dioxide (SiO2) and a symmetric gate stack (GS) of HfO 2-SiO 2.
Abstract: In this paper an Underlap Double Gate (U-DG) Symmetric Heterojunction AlGaN/GaN Metal Oxide Semiconductor High Electron Mobility Transistor (MOS-HEMT) with gate oxide materials of different dielectric constant has been studied using gate oxide materials such as Hafnium dioxide (HfO2), Silicon dioxide (SiO2) and a symmetric gate stack (GS) of HfO2-SiO2. In this work, the analog performance of the devices has been studied on the basis of parameters like transconductance (gm), transconductance generation factor (gm/ID) and intrinsic gain (gmR0). This paper depicts the effect of varying oxide materials on the analog and RF figure of merits (FOMs) such as the gate to drain capacitance (CGD), gate to source capacitance (CGS) and total gate capacitance (CGG), intrinsic resistances, cut-off frequency (fT) and maximum frequency of oscillation (fMAX) using non-quasi-static approach. Studies show that the introduction of a gate oxide layer in the MOS-HEMT device increases the gate controllability reducing gate leakage currents improving RF performance. U-DG AlGaN/GaN MOS-HEMT with HfO2 gate dielectric shows superior Power output efficiency (POE) of 55% compared to the HfO2-SiO2 composite structure and SiO2 with 26% and 20% respectively.
17 citations
Cites result from "Performance of AlGaN/GaN metal-insu..."
...MOS-HEMTs reduces the gate leakage current, higher breakdown voltage [15] and higher cut frequency compared to the Schottky-gate HEMTs [16, 17]....
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TL;DR: In this paper, low-frequency noise (LFN) in ungated two-terminal devices and heterojunction field-effect transistors (HFETs) was investigated.
Abstract: We have systematically investigated low-frequency noise (LFN) in AlN/AlGaN/GaN metal-insulator-semiconductor (MIS) devices, where the AlN gate insulator layer was sputtering-deposited on the AlGaN surface, in comparison with LFN in AlGaN/GaN Schottky devices. By measuring LFN in ungated two-terminal devices and heterojunction field-effect transistors (HFETs), we extracted LFN characteristics in the intrinsic gated region of the HFETs. Although there is a bias regime of the Schottky-HFETs in which LFN is dominated by the gate leakage current, LFN in the MIS-HFETs is always dominated by only the channel current. Analyzing the channel-current-dominated LFN, we obtained Hooge parameters α for the gated region as a function of the sheet electron concentration ns under the gate. In a regime of small ns, both the MIS- and Schottky-HFETs exhibit α∝ns−1. On the other hand, in a middle ns regime of the MIS-HFETs, α decreases rapidly like ns−ξ with ξ ∼ 2-3, which is not observed for the Schottky-HFETs. In addition, ...
10 citations
TL;DR: Using aluminum titanium oxide (AlTiO), an alloy of Al2O3 and TiO2, as a high-k gate insulator, this article fabricated and investigated AlTiO/AlGaN/GaN metal-insulator-semiconductor heterojunction field effect transistors.
Abstract: Using aluminum titanium oxide (AlTiO, an alloy of Al2O3 and TiO2) as a high-k gate insulator, we fabricated and investigated AlTiO/AlGaN/GaN metal-insulator-semiconductor heterojunction field-effect transistors From current low-frequency noise (LFN) characterization, we find Lorentzian spectra near the threshold voltage, in addition to 1/f spectra for the well-above-threshold regime The Lorentzian spectra are attributed to electron trapping/detrapping with two specific time constants, ∼25 ms and ∼3 ms, which are independent of the gate length and the gate voltage, corresponding to two trap level depths of 05–07 eV with a 006 eV difference in the AlTiO insulator In addition, gate leakage currents are analyzed and attributed to the Poole-Frenkel mechanism due to traps in the AlTiO insulator, where the extracted trap level depth is consistent with the Lorentzian LFN
9 citations
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TL;DR: In this article, the authors show that the cause of current collapse is a charging up of a second virtual gate, physically located in the gate drain access region, thus acting as a negatively charged virtual gate.
Abstract: GaN based HFETs are of tremendous interest in applications requiring high power at microwave frequencies. Although excellent current-voltage (I-V) characteristics and record high output power densities at microwave frequencies have been achieved, the origin of the 2DEG and the factors limiting the output power and reliability of the devices under high power operation remain uncertain. Drain current collapse has been the major obstacle in the development of reliable high power devices. We show that the cause of current collapse is a charging up of a second virtual gate, physically located in the gate drain access region. Due to the large bias voltages present on the device during a microwave power measurement, surface states in the vicinity of the gate trap electrons, thus acting as a negatively charged virtual gate. The maximum current available from a device during a microwave power measurement is limited by the discharging of this virtual gate. Passivated devices located adjacent to unpassivated devices on the same wafer show almost no current collapse, thus demonstrating that proper surface passivation prevents the formation of the virtual gate. The possible mechanisms by which a surface passivant reduces current collapse and the factors affecting reliability and stability of such a passivant are discussed.
1,334 citations
07 Nov 2002
TL;DR: This paper reviews the various trapping phenomena observed in SiC- and GaN-based FETs that contribute to compromised power performance and the measurement techniques utilized to identify these traps.
Abstract: It is well known that trapping effects can limit the output power performance of microwave field-effect transistors (FETs). This is particularly true for the wide bandgap devices. In this paper we review the various trapping phenomena observed in SiC- and GaN-based FETs that contribute to compromised power performance. For both of these material systems, trapping effects associated with both the surface and with the layers underlying the active channel have been identified. The measurement techniques utilized to identify these traps and some of the steps taken to minimize their effects, such as modified buffer layer designs and surface passivation, are described. Since similar defect-related phenomena were addressed during the development of the GaAs technology, relevant GaAs work is briefly summarized.
466 citations
TL;DR: In this article, the authors used reactive-sputtered high electron mobility transistors (HfO2) as the gate dielectric and the surface passivation layer, and showed that the gate leakage current is at least five orders of magnitude lower than that of the reference HEMTs.
Abstract: We report the studies of AlGaN∕GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) using reactive-sputtered HfO2 as the gate dielectric and the surface passivation layer. X-ray photoemission method reveals a conduction-band offset of 1.71eV for the HfO2∕GaN heterostructure. The dielectric constant of HfO2 is estimated to be 21 by capacitance-voltage measurements. MOS-HEMTs with a 1.5-μm-long gate exhibit a maximum drain current of 830mA∕mm and a peak transconductance of 115mS∕mm, while the gate leakage current is at least five orders of magnitude lower than that of the reference HEMTs. Good surface passivation effects of HfO2 have also been confirmed by pulsed gate measurements, with MOS-HEMTs showing a significant drain current recovery from current collapse observed in HEMTs.
181 citations
TL;DR: In this paper, the temperature dependencies of the two-dimensional electron gas (2DEG) mobility have been systematically measured for the samples with different 2DEG densities, with the lower decrease ratio at higher temperatures.
Abstract: Electron transport properties in the Al0.15Ga0.85N/GaN heterostructure field effect transistors (HFETs) have been examined from room temperature up to 400 °C. The temperature dependencies of the two-dimensional electron gas (2DEG) mobility have been systematically measured for the samples with different 2DEG densities. The 2DEG mobility has been shown to decrease with increasing the temperature, with the lower decrease ratio at higher temperatures, and moreover, shown to be less dependent on the 2DEG density at higher temperatures. These features well agree with those of the longitudinal optical phonon-limited mobility theoretically predicted, although the effect of alloy and interface scattering should further be examined and analyzed. The observed 2DEG mobilities at 400 °C were as high as from 100 to 120 cm2/V s, directly providing the evidence for suitability of the HFET of this material system for high-temperature applications. Moreover, Si-doped Al0.15Ga0.85N single layer has been shown to exhibit a ...
110 citations
TL;DR: In this paper, a frequency dependent capacitance and conductance analysis of the AlGaN/GaN-Si heterostructure field-effect transistors (HFETs) and Al2O3/AlGaN, GaN, Si metal-oxide-semiconductor (MOSHFET) was performed to investigate the trap effects in these devices.
Abstract: We report on frequency dependent capacitance and conductance analysis of the AlGaN/GaN/Si heterostructure field-effect transistors (HFETs) and Al2O3/AlGaN/GaN/Si metal-oxide-semiconductor HFETs (MOSHFETs) in order to investigate the trap effects in these devices. The capacitance of the HFETs exhibits significantly higher frequency dispersion than that of the MOSHFETs. Two different types of traps were found from the conductance analysis on both types of devices, fast with the time constant τ≅(0.1–1) μs and slow with τ=8 ms. The density of trap states evaluated on the HFETs was DT≅2.5×1012 and up to 1013 cm−2 eV−1 for the fast and slow traps, respectively. Analysis of the MOSHFETs yielded only slightly lower DT of the fast traps (≅1.5×1012 cm−2 eV−1), but nearly two orders of magnitude lower density of slow traps (≤4×1011 cm−2 eV−1) than those of the HFETs. This indicates an effective passivation of slow surface related traps but less influence on fast (probably bulk related) trapping states by applying an insulator on the AlGaN/GaN HFET.
102 citations