Mechanism of the reverse gate leakage in AlGaN/GaN high electron mobility transistors
TL;DR: In this article, the off-state gate current in AlGaN/GaN high electron mobility transistors is shown to arise from two parallel gate to substrate tunneling paths: a direct path, and a path via deep traps.
Abstract: The off-state gate current in AlGaN/GaN high electron mobility transistors is shown to arise from two parallel gate to substrate tunneling paths: a direct path, and a path via deep traps, which are distributed throughout the AlGaN layer and spread over an energy band. A model to calculate this current is given, which shows that trap-assisted tunneling dominates below T∼500 K, and direct tunneling (thermionic field emission) dominates at higher temperatures. A model fit to experimental results yields the following fabrication process sensitive parameters: trap concentration of ∼1013–1015 cm−3, and trap bandwidth of ∼50%–70% of the barrier height located 0.4–0.55 V below the conduction band edge.
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TL;DR: In this paper, a method with an accurate control of threshold voltages of AlGaN/GaN high-electron mobility transistors (HEMTs) using a fluoride-based plasma treatment was presented.
Abstract: This paper presents a method with an accurate control of threshold voltages (Vth) of AlGaN/GaN high-electron mobility transistors (HEMTs) using a fluoride-based plasma treatment. Using this method, the Vth of AlGaN/GaN HEMTs can be continuously shifted from -4 V in a conventional depletion-mode (D-mode) AlGaN/GaN HEMT to 0.9 V in an enhancement-mode AlGaN/GaN HEMT. It was found that the plasma-induced damages result in a mobility degradation of two-dimensional electron gas. The damages can be repaired and the mobility can be recovered by a post-gate annealing step at 400 degC. At the same time, the shift in Vth shows a good thermal stability and is not affected by the post-gate annealing. The enhancement-mode HEMTs show a performance (transconductance, cutoff frequencies) comparable to the D-mode HEMTs. Experimental results confirm that the threshold-voltage shift originates from the incorporation of F ions in the AlGaN barrier. In addition, the fluoride-based plasma treatment was also found to be effective in lowering the gate-leakage current, in both forward and reverse bias regions. A physical model of the threshold voltage is proposed to explain the effects of the fluoride-based plasma treatment on AlGaN/GaN HEMTs
489 citations
TL;DR: In this paper, the mechanism of leakage currents through GaN and AlGaN Schottky interfaces is discussed based on detailed temperature-dependent current-voltage (I-V-T) measurements.
Abstract: Based on detailed temperature-dependent current–voltage (I–V–T) measurements the mechanism of leakage currents through GaN and AlGaN Schottky interfaces is discussed. The experiments were compared to calculations based on thin surface barrier model in which the effects of surface defects were taken into account. Our simulation method reproduced the experimental I–V–T characteristics of the GaN and AlGaN Schottky diodes, and gave excellent fitting results to the reported Schottky I–V curves in GaN for both forward and reverse biases at different temperatures. The present results indicate that the barrier thinning caused by unintentional surface-defect donors enhances the tunneling transport processes, leading to large leakage currents through GaN and AlGaN Schottky interfaces.
192 citations
TL;DR: In this article, the authors summarize the current understanding of the gate leakage current and current collapse mechanisms, where awareness of the surface defects is the key to controlling and improving device performance.
Abstract: GaN and AlGaN have shown great potential in next-generation high-power electronic devices; however, they are plagued by a high density of interface states that affect device reliability and performance, resulting in large leakage current and current collapse. In this review, the authors summarize the current understanding of the gate leakage current and current collapse mechanisms, where awareness of the surface defects is the key to controlling and improving device performance. With this in mind, they present the current research on surface states on GaN and AlGaN and interface states on GaN and AlGaN-based heterostructures. Since GaN and AlGaN are polar materials, both are characterized by a large bound polarization charge on the order of 1013 charges/cm2 that requires compensation. The key is therefore to control the compensation charge such that the electronic states do not serve as electron traps or affect device performance and reliability. Band alignment modeling and measurement can help to determi...
179 citations
TL;DR: In this paper, the authors describe critical issues and problems including leakage current, current collapse and threshold voltage instability in high-electron-mobility transistors (HEMTs) using oxides, nitrides and high-κ dielectrics.
Abstract: Recent years have witnessed GaN-based devices delivering their promise of unprecedented power and frequency levels and demonstrating their capability as an able replacement for Si-based devices. High-electron-mobility transistors (HEMTs), a key representative architecture of GaN-based devices, are well-suited for high-power and high frequency device applications, owing to highly desirable III-nitride physical properties. However, these devices are still hounded by issues not previously encountered in their more established Siand GaAs-based devices counterparts. Metal–insulator–semiconductor (MIS) structures are usually employed with varying degrees of success in sidestepping the major problematic issues such as excessive leakage current and current instability. While different insulator materials have been applied to GaN-based transistors, the properties of insulator/III-N interfaces are still not fully understood. This is mainly due to the difficulty of characterizing insulator/AlGaN interfaces in a MIS HEMT because of the two resulting interfaces: insulator/AlGaN and AlGaN/GaN, making the potential modulation rather complicated. Although there have been many reports of low interface-trap densities in HEMT MIS capacitors, several papers have incorrectly evaluated their capacitance–voltage (C–V) characteristics. A HEMT MIS structure typically shows a 2-step C–V behavior. However, several groups reported C–V curves without the characteristic step at the forward bias regime, which is likely to the high-density states at the insulator/ AlGaN interface impeding the potential control of the AlGaN surface by the gate bias. In this review paper, first we describe critical issues and problems including leakage current, current collapse and threshold voltage instability in AlGaN/GaN HEMTs. Then we present interface properties, focusing on interface states, of GaN MIS systems using oxides, nitrides and high-κ dielectrics. Next, the properties of a variety of AlGaN/GaN MIS structures as well as different characterization methods, including our own photo-assisted C–V technique, essential for understanding and developing successful surface passivation and interface control schemes, are given in the subsequent section. Finally we highlight the important progress in GaN MIS interfaces that have recently pushed the frontier of nitride-based device technology.
163 citations
TL;DR: In this paper, high-electric-field degradation phenomena are investigated in GaN-capped AlGaN/GaN HEMTs by comparing experimental data with numerical device simulations.
Abstract: High-electric-field degradation phenomena are investigated in GaN-capped AlGaN/GaN HEMTs by comparing experimental data with numerical device simulations. Under power- and OFF-state conditions, 150-h DC stresses were carried out. Degradation effects characterizing both stress experiments were as follows: a drop in the dc drain current, the amplification of gate-lag effects, and a decrease in the reverse gate leakage current. Numerical simulations indicate that the simultaneous generation of surface (and/or barrier) and buffer traps can account for all of the aforementioned degradation modes. Experiments also showed that the power-state stress induced a drop in the transconductance at high gate-source voltages only, whereas the OFF-state stress led to a uniform transconductance drop over the entire gate-source-voltage range. This behavior can be reproduced by simulations provided that, under the power-state stress, traps are assumed to accumulate over a wide region extending laterally from the gate edge toward the drain contact, whereas, under the OFF-state stress, trap generation is supposed to take place in a narrower portion of the drain-access region close to the gate edge and to be accompanied by a significant degradation of the channel transport parameters.
130 citations
References
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01 Jan 1978TL;DR: In this article, a review of the present knowledge of metal-semiconductor contacts is given, including the factors that determine the height of the Schottky barrier, its current/voltage characteristics, and its capacitance.
Abstract: A review is given of our present knowledge of metal-semiconductor contacts. Topics covered include the factors that determine the height of the Schottky barrier, its current/voltage characteristics, and its capacitance. A short discussion is also given of practical contacts and their application in semiconductor technology, and a comparison is made with p-n junctions.
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01 Jan 2001
TL;DR: The Brillouin Zone for Wurtzite Crystal is defined in this paper, as the first zone for Zinc Blende Crystal, which is a type of hexagonal crystal.
Abstract: Contributors. Preface. Gallium Nitride (GaN) (V. Bougrov, et al.). Aluminum Nitride (AIN) (Y. Goldberg). Indium Nitride (InN) (A. Zubrilov). Boron Nitride (BN) (S. Rumyantsev, et al.). Silicon Carbide (SiC) (Y. Goldberg, et al.). Silicon-Germanium (Si-1-xGe-x) (F. Schaffler). Appendix 1: Basic Physical Constants. Appendix 2: Periodic Table of the Elements. Appendix 3: Rectangular Coordinates for Hexagonal Crystal. Appendix 4: The First Brillouin Zone for Wurtzite Crystal. Appendix 5: Zinc Blende Structure. Appendix 6: The First Brillouin Zone for Zinc Blende Crystal. Additional References.
1,556 citations
TL;DR: In this paper, the use of an AlGaN layer with high Al mole-fraction is proposed to increase the equivalent figures of merit of the Al-GaN/GaN MODFET structure.
Abstract: The use of an AlGaN layer with high Al mole-fraction is proposed to increase the equivalent figures of merit of the AlGaN/GaN MODFET structure. It is shown that the room temperature mobility has little degradation with increasing Al mole-fraction up to 50%. 0.7-/spl mu/m gate-length Al/sub 0.5/Ga/sub 0.5/N/GaN MODFETs by optical lithography exhibit a current density of 1 A/mm and three-terminal breakdown voltages up to 200 V. These devices on sapphire substrates without thermal management also show CW power densities of 2.84 and 2.57 W/mm at 8 and 10 GHz, respectively, representing a marked performance improvement for GaN-based FETs.
305 citations
TL;DR: In this paper, the gate leakage currents in AlGaN/GaN heterostructure field effect transistor (HFET) structures with conventional and polarization-enhanced barriers have been studied.
Abstract: Gate leakage currents in AlGaN/GaN heterostructure field-effect transistor (HFET) structures with conventional and polarization-enhanced barriers have been studied Comparisons of extensive gate leakage current measurements with two-dimensional simulations show that vertical tunneling is the dominant mechanism for gate leakage current in the standard-barrier HFET and that the enhanced-barrier structure suppresses this mechanism in order to achieve a reduced leakage current An analytical model of vertical tunneling in a reverse-biased HFET gate-drain diode is developed to evaluate the plausibility of this conclusion The model can be fit to the measured data, but suggests that additional leakage mechanisms such as lateral tunneling from the edge of the gate to the drain or defect-assisted tunneling also contribute to the total leakage current The vertical tunneling current mechanism is shown to be more significant to the gate leakage current in III–V nitride HFETs than in HFETs fabricated in other III–V
194 citations