Low Reverse Leakage Current Research Articles

Enhanced current transport and injection in thin-film gallium-nitride light-emitting diodes by laser-based doping.

This paper reports improvements in the electrical and optical properties of blue-emission gallium nitride (GaN)-based thin-film light-emitting diodes (TFLEDs) after laser-based Si doping (LBSD) of a nitrogen-face n-GaN (denoted as hereafter n-GaN) layer. Experimental results show that the light-output powers of the flat- and rough-surface TFLEDs after LBSD are 52.1 and 11.35% higher than those before LBSD, respectively, at a current of 350 mA, while the corresponding operating voltages are decreased by 0.22 and 0.28 V for the flat- and rough-surface TFLEDs after LBSD, respectively. The reduced operating voltage after LBSD of the top n-GaN layer may result from the remarkably decreased specific contact resistance at the metal/n-GaN interface and the low series resistance of the TFLED device. The LBSD of n-GaN increases the number of nitrogen vacancies, and Si substitutes for Ga (SiGa) at the metal/n-GaN interface to produce highly Si-doped regions in n-GaN, leading to a decrease in the Schottky barrier height and width. As a result, the specific contact resistances are significantly decreased to 1.56 × 10(-5) and 2.86 × 10(-5) Ω cm(2) for the flat- and rough-surface samples after LBSD, respectively. On the other hand, the increased light-output power after LBSD can be explained by the uniform current spreading, efficient current injection, and enhanced light scattering resulting from the low contact resistivity, low lateral current resistance, and additional textured surface, respectively. Furthermore, LBSD did not degrade the electrical properties of the TFLEDs owing to low reverse leakage currents. The results indicate that our approach could potentially enable high-efficiency and high-power capabilities for optoelectronic devices.

Lateral trench oxide Schottky rectifier on SOI for power integrated circuits

In this paper, a Lateral Trench Oxide Schottky (LTOS) rectifier on silicon-on-insulator suitable for power integrated circuits is presented. The proposed structure utilizes a surface Schottky contact with vertical field-plate placed in a trench filled with oxide. The field-plate reduces the electric field on the Schottky contact and suppresses the barrier lowering effect leading to significant improvement in the device performance. Further, the proposed structure folds the drift region in vertical and horizontal directions resulting substantial reduction in pitch length of the device. Two-dimensional numerical simulations have been performed to analyse and optimize the performance of proposed device and results are compared with that of the conventional lateral Schottky rectifier. The LTOS rectifier provides 60 % improvement in breakdown voltage and 50 % reduction in pitch length as compared to the conventional device while maintaining low forward voltage drop and low reverse leakage current.

Effects of Electrostatic Discharge Stress on Current-Voltage and Reverse Recovery Time of Fast Power Diode

Fast recovery diodes (FRDs) were developed using the <TEX>$p^{{+}{+}}/n^-/n^{{+}{+}}$</TEX> epitaxial layers grown by low temperature epitaxy technology. We investigated the effect of electrostatic discharge (ESD) stresses on their electrical and switching properties using current-voltage (I-V) and reverse recovery time analyses. The FRDs presented a high breakdown voltage, >450 V, and a low reverse leakage current, < <TEX>$10^{-9}$</TEX> A. From the temperature dependence of thermal activation energy, the reverse leakage current was dominated by thermal generation-recombination and diffusion, respectively, at low and high temperature regions. By virtue of the abrupt junction and the Pt drive-in for the controlling of carrier lifetime, the soft reverse recovery behavior could be obtained along with a well-controlled reverse recovery time of 21.12 ns. The FRDs exhibited excellent ESD robustness with negligible degradations in the I-V and the reverse recovery characteristics up to <TEX>${\pm}5.5$</TEX> kV of HBM and <TEX>${\pm}3.5$</TEX> kV of IEC61000-4-2 shocks. Likewise, transmission line pulse (TLP) analysis reveals that the FRDs can handle the maximum peak pulse current, <TEX>$I_{pp,max}$</TEX>, up to 30 A in the forward mode and down to - 24 A in the reverse mode. The robust ESD property can improve the long term reliability of various power applications such as automobile and switching mode power supply.

In situ SiNx gate dielectric by MOCVD for low‐leakage‐current ultra‐thin‐barrier AlN/GaN MISHEMTs on Si

In situ SiNx grown by metal‐organic chemical vapor deposition (MOCVD) was employed as the gate dielectric for ultra‐thin‐barrier AlN/GaN metal‐insulator‐semiconductor high electron mobility transistors (MISHEMTs) on Si substrates. Despite the ultra‐thin barrier of 1.5 nm, low reverse leakage current of below 10−7 A cm−2 was obtained with a 7 nm in situ SiNx gate dielectric. The good surface passivation effects of in situ SiNx were also demonstrated by the enhanced source/drain (S/D) current density and the reduced drain current degradation. Furthermore, interface trapping effects in the in situ SiNx/AlN/GaN heterostructures were investigated by double‐mode capacitance–voltage (C–V) measurements and frequency dependent conductance analysis. A trap states density of 1.9–3.4 × 1012 cm−2 eV−1 with a time constant of 0.8–17 µs were deduced.

Transport properties of SiO2/AlInN/AlN/GaN metal–oxide–semiconductor high electron mobility transistors on SiC substrate

Unpassivated SiO2/AlInN/AlN/GaN metal–oxide–semiconductor high electron mobility transistors (MOSHEMTs) exhibiting a thin barrier layer are investigated with a particular focus on their dc characteristics dependence on the gate length. The epiwafer exhibits a sheet resistance of ∼250 Ω/□ and a channel charge density of 7.4 × 1012 cm−2 deduced from the 1 MHz capacitance–voltage curves. The results indicate that the thickness of the AlInN barrier can be reduced below 5 nm without degradation of the insulated gate devices performance. For transistors with gate lengths (LG) between 1.8 and 2.0 µm, dc drain saturation currents densities as high as 1.8 A mm−1 are achieved at +4 V gate–source bias (VGS) with very low reverse gate leakage currents. The electron zero-bias drift mobility was determined to be 1670 cm2 V−1 s−1 from the low-field channel conductance measurements. On the other side, using an analytical model it is found that the maximum output current density at VGS = 0 V can be enhanced by ∼23% when LG is scaled from 1.8 µm down to 100 nm. With further improvement of the quality of the gate insulating oxide layer and the implementation of surface passivation, both with the aim of suppressing the observed current collapse, the presented results suggest that these MOSHEMTs could become very attractive for the realization of high-power electronics.

Leakage current analysis of diamond Schottky barrier diodes operated at high temperature

Diamond is a promising material for use in high-power semiconductor devices that are operated under high-temperature conditions. A Schottky barrier diode (SBD) fabricated by using high-quality diamond shows a low reverse leakage current of less than 10−7 A/cm2 in a reverse electrical field of 1.5 MV/cm at room temperature. The leakage current of this diamond SBD is found to be low even at an elevated temperature of 415 K. The leakage current of this diamond SBD is 2–4 orders of magnitude lower than that of a SiC SBD owing to the larger barrier height. The leakage characteristics of the diamond SBD are modeled using the thermionic-field emission model, which well agrees with experimental results.

InGaN/GaN blue light emitting diodes grown on Si(110) and Si(111) substrates

In this paper, InGaN/GaN multiple quantum-well blue light emitting diodes (LEDs) are successfully grown on Si(110) and Si(111) substrates. The micro-structural properties of the LEDs are characterized by means of high-resolution X-ray diffraction, atomic force microscopy, Raman spectra, and temperature dependent photoluminescence measurements. The results show that the sample on Si(110) substrate exhibits the high crystal quality, weak tensile strain, and large internal quantum efficiency. The optoelectronic properties of the LED devices are also investigated. The I-V curves indicate that the LED devices fabricated on Si(110) and Si(111) substrates have similar series resistances and low reverse leakage currents, but the LED devices fabricated on Si(110) substrate possess lower turn-on voltages. The relationship between light output intensity and injection current suggests that the LED device fabricated on Si(110) substrate has a strong light output efficiency. The study on the variation of spectral peak energy with injection current of the LED device reveals that LED device on Si(110) substrate presents a smaller spectral shift range when increasing the injection current. And the smaller spectral shift range reflects the weak quantum-confined Stark effect in the device, which can be attributed to the high crystal quality and weak strain between well layer and barrier film in the LED sample grown on Si(110).

Design of polarization-dipole-induced isotype heterojunction diodes for use in III–N hot electron transistors

The design of III–nitride-based hot electron transistors (HETs) is investigated using different diode design methodologies. Barrier-limited forward bias current and low reverse leakage current are demonstrated for the emitter-base diode using a barrier formed by a high-Al% AlGaN layer as a polarization-dipole layer. Two different base-collector diode designs are compared, one using 30% AlGaN as the barrier and the other using 10% InGaN as a polarization-dipole barrier. The InGaN polarization-dipole approach is shown to exhibit much lower reverse leakage currents. The impact of threading dislocation density on diode characteristics is also discussed.

Au-Free AlGaN/GaN Power Diode on 8-in Si Substrate With Gated Edge Termination

High-performance AlGaN/GaN diodes are realized on 8-in Si wafers with Au-free CMOS-compatible technology. The diodes are cointegrated on the same substrate together with the AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors and with only one extra lithographic step. The diode anode and the transistor gate are processed together and the same metallization is used for both, avoiding extra metal deposition dedicated to the Schottky junction. A gated edge termination allows obtaining low reverse leakage current (within 1 μA/mm at -600 V), which is several orders of magnitude lower than the one of conventional Schottky diodes processed on the same wafer. Recess is implemented at the anode, resulting in low diode turn-on voltage values.

AlGaN/GaN high-electron-mobility transistors with transparent gates by Al-doped ZnO

AlGaN/GaN high-electron-mobility transistors (HEMTs) with Al-doped ZnO (AZO) transparent gate electrodes are fabricated, and Ni/Au/Ni-gated HEMTs are produced in comparison. The AZO-gated HEMTs show good DC characteristics and Schottky rectifying characteristics, and the gate electrodes achieve excellent transparencies. Compared with Ni/Au/Ni-gated HEMTs, AZO-gated HEMTs show a low saturation current, high threshold voltage, high Schottky barrier height, and low gate reverse leakage current. Due to the higher gate resistivity, AZO-gated HEMTs exhibit a current—gain cutoff frequency (fT) of 10 GHz and a power gain cutoff frequency (fmax) of 5 GHz, and lower maximum oscillation frequency than Ni/Au/Ni-gated HEMTs. Moreover, the C—V characteristics are measured and the gate interface characteristics of the AZO-gated devices are investigated by a C—V dual sweep.

On an Electroless Plating (EP)-Based Pd/AlGaN/GaN Heterostructure Field-Effect Transistor (HFET)-Type Hydrogen Gas Sensor

A Pd/AlGaN/GaN heterostructure field-effect transistor (HFET)-type hydrogen gas sensor, based on the sensitization, activation, and electroless plating (EP) deposition processes, is fabricated and studied. Due to the used sensitization and activation approaches, a dense and uniform EP seed layer could be achieved. Good dc and microwave characteristics, including the higher turn-on voltage, lower reverse leakage current, improved thermal stability of drain current, enhanced unity current gain cutoff frequency, and maximum oscillation frequency, are obtained for a 1-m-gate-length device. Moreover, the significant hydrogen gas sensing performance, such as larger drain current variation and higher hydrogen detection sensitivity, are found under 1% and 5 ppm H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /air ambiences, respectively. Consequently, the studied EP-based Pd/AlGaN/GaN HFET gives the promise for high-performance electronic device and hydrogen gas sensor applications.

Fabrication and characterization of InAlN/GaN-based double-channel high electron mobility transistors for electronic applications

In our previous work [J. S. Xue et al., Appl. Phys. Lett. 100, 013507 (2012)], superior electron-transport properties are obtained in InAlN/GaN/InAlN/GaN double-channel (DC) heterostructures grown by pulsed metal organic chemical vapor deposition (PMOCVD). In this paper, we present a detailed fabrication and systematic characterization of high electron mobility transistors (HEMTs) fabricated on these heterostructures. The device exhibits distinct DC behavior concerning with both static-output and small-signal performance, demonstrating an improved maximum drain current density of 1059 mA/mm and an enhanced transconductance of 223 mS/mm. Such enhancement of device performance is attributed to the achieved low Ohmic contact resistance as low as 0.33 ± 0.05 Ω·mm. Moreover, very low gate diode reverse leakage current is observed due to the high quality of InAlN barrier layer deposited by PMOCVD. A current gain frequency of 10 GHz and a maximum oscillation frequency 21 GHz are also observed, which are comparable to the state-of-the-art AlGaN/GaN-based DC HEMT found in the literature. The results demonstrate the great potential of PMOCVD for application in InAlN-related device’s epitaxy.

Shottky Barrier Diodes on AlN Free-Standing Substrates

Lateral Schottky rectifiers were fabricated on bulk single-crystal free-standing AlN substrates. The unintentionally doped substrates display n-type conductivity. The diode shows a low reverse leakage current of ∼0.1 nA at -40 V at room temperature. The ideality factor for forward characteristics is 11.7 at room temperature and shows temperature dependence, suggesting the lateral nonuniformities at the metal/semiconductor interface. The fabricated devices are stably operated even at 573 K, owing to the wide band gap (6.2 eV) of AlN. The reverse leakage current of the device is explained by either a trap-assisted tunneling process or one-dimensional variable-range-hopping conduction along the dislocations.

Silicon-Germanium multi-quantum well photodetectors in the near infrared

Single crystal Silicon-Germanium multi-quantum well layers were epitaxially grown on silicon substrates. Very high quality films were achieved with high level of control utilizing recently developed MHAH epitaxial technique. MHAH growth technique facilitates the monolithic integration of photonic functionality such as modulators and photodetectors with low-cost silicon VLSI technology. Mesa structured p-i-n photodetectors were fabricated with low reverse leakage currents of ~10 mA/cm² and responsivity values exceeding 0.1 A/W. Moreover, the spectral responsivity of fabricated detectors can be tuned by applied voltage.

Ohmic and rectifying contacts on bulk AlN for radiation detector applications

AbstractIn this paper we report on ohmic and rectifying contacts fabricated on undoped bulk AlN substrates for radiation detector applications. The ohmic Ni contacts exhibit negligible contact resistances. Current conduction is dominated by field enhanced thermal emission from traps 0.4 to 0.6 eV below the conduction band. The Pt Schottky contacts show excellent rectifying behaviour. In forward conduction, device current is again limited by the Poole‐Frenkel effect. The Schottky barrier features very low reverse leakage currents, and voltages of up to ‐200 V can be applied. The capability of bulk AlN for radiation detectors at room temperature is demonstrated. Suitability is deduced from both X‐ray absorption experiments and low reverse leakage currents of the fabricated Schottky diodes. Additionally, the AlN substrate is almost blind to sun light due to its wide band gap. Still, reduction of recombination sites in AlN is required to achieve maximum detector performance. (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

InGaN photodiodes using CaF2 insulator for high‐temperature UV detection

AbstractThe authors report on a thermally‐stable ultraviolet‐A photodiode using CaF2 as the insulation layer in the metal‐insulator‐semiconductor (MIS) structure based on a high‐quality InGaN film. Compared to the Schottky photodiode (SPD) without the insulator, the MIS‐SPD device maintains a low reverse leakage current, a high photo‐to‐dark current ratio and fast response at the temperature as high as 523 K, indicating CaF2 as a good candidate for the III‐Nitride devices. The overall photoresponse properties of the MIS‐SPD are governed by the metal/insulator/semiconductor interfaces. The photocurrent gain at reverse biases from room‐temperature to 463 K is interpreted in term of thermionic‐field emission (TFE) and field emission mechanism, while TFE becomes the dominant mechanism at higher temperatures (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Investigation of nano patches in Ni/n-Si micro Schottky diodes with new aspect

High-quality Ni/n-Si Schottky barrier diodes (SBDs) with low reverse leakage current were produced using a molybdenum (metal) mask. An identical preparation of the diodes shows a diode-to-diode variation in the ideality factor and barrier height parameters. Topological, phase and potential distribution investigations of the surface before and after preparation of the thin metal film for ohmic and Schottky contacts with a Conducting Probe Atomic Force Microscope (CP-AFM) show that thin metal film deposited on Ni/n-Si Schottky diode (SD) consists of many nano patches. Investigation of the patches in the ohmic contact side shows that these ohmic contacts also consist of nano patches in the range 20–40 nm with a variation in the potential distribution reaching about 1 V, resulting in different electrical behaviors in different regions of the contact surface. Even with sufficient care in the preparation and cleaning of the contact surface there is a potential difference of about 0.5 V between different parts of the semiconductor surface, which is one of the sources of different electrical behaviors of the substrate. These patches are sets of parallelly connected and electrically cooperating nano contacts with size between 20 and 40 nm. The barrier heights (BH) and ideality factor ( n) are affected by the potential distribution on the surface. There is a spot field between the patches with different local work functions, which are in direct electrical contact with the surrounding patches. It is shown that in the real metal–semiconductor (MS) contacts, patches with quite different configurations, various geometrical sizes and local work functions are randomly distributed on the metal surface. The relation between ideality factor ( n) and potential barrier height (BH) depends on the distribution of patches and their work functions.

Improved Optical and Electrical Characteristics of Free-Standing GaN Substrates by Chemical Polishing Utilizing Photo-Electrochemical Method

The optical and electrical properties of GaN(0001) surfaces treated by a novel chemical polishing method are described. Scanning microscopic photoluminescence images reveal that the polished GaN surface shows improved luminescence properties compared to the untreated surface. Current-voltage measurements of Schottky barriers formed using the GaN substrates show that the polished GaN surface has a lower reverse leakage current, and that the barrier height and ideality factor are improved after the polishing treatment.

Effect of diode size and series resistance on barrier height and ideality factor in nearly ideal Au/n type-GaAs micro Schottky contact diodes

Small high-quality Au/n type-GaAs Schottky barrier diodes (SBDs) with low reverse leakage current are produced using lithography. Their effective barrier heights (BHs) and ideality factors from current-voltage (I–V) characteristics are measured by a Pico ampere meter and home-built I–V instrument. In spite of the identical preparation of the diodes there is a diode-to-diode variation in ideality factor and barrier height parameters. Measurement of topology of a surface of a thin metal film with atomic force microscope (AFM) shows that Au-n type-GaAS SD consists of a set of parallel-connected micro and nanocontacts diodes with sizes approximately in a range of 100–200 nm. Between barrier height and ideality factor there is an inversely proportional dependency. With the diameter of contact increasing from 5 μm up to 200 μm, the barrier height increases from 0.833 up to 0.933 eV and its ideality factor decreases from 1.11 down to 1.006. These dependencies show the reduction of the contribution of the peripheral current with the diameter of contact increasing. We find the effect of series resistance on barrier height and ideality factor.

UV Light-Emitting Diodes at 340 nm Fabricated on a Bulk GaN Substrate

We demonstrate an ultra-violet light-emitting diode (UV-LED) fabricated on a bulk GaN substrate with electroluminescence (EL) emission centered at about 340nm. The UV-LED exhibits low reverse leakage current on the order of 10−9 A under −5 V at room temperature, which can be explained by the low defect density in the epi-structure. The evolution of EL spectra as a function of injection current levels reveals the improved heat dissipation of the LEDs with vertical geometry on the bulk GaN substrate. The unusual increase of EL intensity at elevated temperatures can be explained by thermally assisted p-dopant ionization.