Hydrogen “doped” thin film diamond field effect transistors for high power applications

Early predictions that diamond would be a suitable material for high performance, high power devices were not supported by the characteristics of diodes and field effect transistors (FETs) fabricated on boron doped (p-type) thin film material. In this paper commercially accessible polycrystalline thin film diamond has been turned p-type by the incorporation of near surface hydrogen; mobility values as high as 70 cm² V⁻¹ s⁻¹ have been measured for films with a carrier concentration of 5×10¹⁷ cm⁻³. Schottky diodes and metal–semiconductor FETs (MESFETs) have been fabricated using this approach which display unprecedented performance levels; diodes with a rectification ratio >10⁶, leakage currents <1 nA, no indication of reverse bias breakdown at 100 V and an ideality factor of 1.1 have been made. Simple MESFET structures that are capable of switching V_DS values of 100 V with low leakage and current saturation (pinch-off) characteristics have also been fabricated. Predictions based upon experiments performed on these devices suggest that optimised device structures will be capable of operation at power levels up to 20 W mm⁻¹, implying that thin film diamond may after all be an interesting material for power applications.     

Thin oxide grown on heavily channel-implanted substrate by using a low temperature wafer loading and N2 pre-annealing process

In this paper, we present high integrity thin oxides grown on the channel implanted substrate (3 × 10¹⁷ cm⁻³) and heavily doped substrate (1 × 10²⁰ cm⁻³) by using a low-temperature wafer loading and N₂ pre-annealing process. The presented thin oxide grown on the channel implanted substrate exhibits a very low interface state density (1 × 10¹⁰ cm⁻² eV⁻¹) and a very high intrinsic dielectric breakdown field (15 MV/cm). It also shows a lower charge trapping rate and interface state generation rate than the conventional thermal oxide. For the thin oxide grown on the heavily-doped substrate by using the proposed recipe, the implantation-induced damage close to the silicon surface can be almost annealed out. The presented heavily-doped oxide shows much better dielectric characteristics, such as the dielectric breakdown field and the charge-to-breakdown, as compared to the conventional heavily-doped oxide.     

Estimation for the capture cross-sections of surface state on p-Si surface by photovoltaic method

A new method which can nondestructively measure the surface-state density (SSD) D_s and estimate the capture cross-sections (CCS) of surface state σ⁰_n and σ⁻_p on surface of p-type semiconductor crystals is proposed. This method is based on the photovoltage measurements at various temperatures. The photovoltage experiment was carried out with a (1 1 1) p-type Si single crystal (N_A=4.8×10¹⁴ cm ⁻³). Owing to that the surface barrier height φ_BP=0.6421 V and the surface-recombination velocity s_n=9.6×10³ cm s⁻¹ of this sample can be determined, the SSD D_s=1.2×10¹¹ cm⁻² eV⁻¹ can therefore be obtained, furthermore CCS σ⁰_n≈5×10⁻¹⁴ cm² and σ⁻_p≈2×10⁻¹⁰ cm² can also be estimated. These results are consistent with that of related reports obtained by other methods.     

Gate bias polarity dependence of charge trapping and time-dependentdielectric breakdown in nitrided and reoxidized nitrided oxides

The gate bias polarity dependence of charge trapping and time-dependent dielectric breakdown (TDDB) in nitrided and reoxidized nitrided silicon dioxides prepared by rapid thermal processing (RTP) is reported. Charge trapping during high-field injection can be reduced by rapid thermal nitridation for both substrate and gate injection. While reoxidation of nitrided oxides shows further reduction in charge trapping for substrate injection, degradation is observed for gate injection. Similar effects are observed for TDDB: reoxidized nitrided oxides show charge-to-breakdown in excess of 300 C/cm² for substrate injection, but less than 30 C/cm² for gate injection. These effects are related to the nitrogen and hydrogen profiles in the oxides. By tailoring the process conditions, a symmetric behavior of NO and RONO films with low charge trappings and Q _BD in excess of 50 C/cm² is possible, making them attractive as long-lifetime dielectrics from EEPROM (electrically erasable programmable ROM) and flash EEPROM technologies     

Trap density of silicon chlorine oxides

By measuring the ramp voltage I–V characteristics, we obtained the oxide trap density and capture cross-section for (O₂ + HCl) dry oxidized samples in the temperature range 900–1100°C. It was found that the oxide trap density increases with an increase in the oxidation temperature. The activation energy of oxide trap incorporation is of the order of 4 eV. The capture cross-section determined for the oxide traps is of the order of 10⁻¹⁴ cm².     

Uniformity and high temperature performance of X-band nitride power HEMTs fabricated from 2-inch epitaxy

X-band performance, high temperature D.C. operation and uniformity have been evaluated for 1 μm gate AlGaN/GaN HEMTs grown by RF atomic nitrogen plasma MBE. Deposition and fabrication were performed on 2-inch (0001) sapphire substrates to determine process uniformity. HEMTs with 300 μm total gate width and dual gate finger geometry have been fabricated with 650–700 cm² V⁻¹×s mobility. Maximum frequency cut-offs on the order of 8–10 GHz were achieved. D.C. performance at room temperature was >500 mA mm⁻¹, and external transconductance was >70 mS mm⁻¹. The transistors operated at test temperatures of 425°C in air.     

Electrical properties of N2O/NH3 plasma grownoxynitride on strained-Si

Growth of ultrathin (<100 Å) oxynitride on strained-Si using microwave N₂O and NH₃ plasma is reported. X-ray photoelectron spectroscopy (XPS) results indicate a nitrogen-rich layer at the strained-Si/SiO₂ interface. The electrical properties of oxynitrides have been characterized using a metal-insulator-semiconductor (MIS) structure. A moderately low value of insulator charge density (6.1×10¹⁰ cm^-2) has been obtained for NH₃ plasma treated N₂O oxide sample. Nitrided oxide shows a larger breakdown voltage and an improved charge trapping properties under Fowler-Nordheim (F-N) constant current stress     

Process and device characterization of high voltage gallium arsenide P-i-N layers grown by an improved liquid phase epitaxy method

GaAs P-i-N layers with an i-region net doping of less than 10¹² cm⁻³ were grown on P⁺ and N⁺ substrates by a modified liquid phase epitaxy (LPE) method. Doping profiles and structural data obtained by varius characterization techniques are presented and discussed. A P⁺-P-i-N-N⁺ diode with a 25 μm-wide i-region exhibits a breakdown voltage of 1000 V, a t_rr of 50 ns, and reverse current densities (at V_R = 800 V) of − 3 × 10⁻⁶ A/cm² at 25°C and 10⁻² A/cm² at 260° C.     

Effect of bottom electrode materials on the electrical andreliability characteristics of (Ba, Sr)TiO3 capacitors

The dielectric constant and the leakage current density of (Ba, Sr)TiO₃ (BST) thin films deposited on various bottom electrode materials (Pt, Ir, IrO₂/Ir, Ru, RuO₂/Ru) before and after annealing in O₂ ambient were investigated. The improvement of crystallinity of BST films deposited on various bottom electrodes was observed after the postannealing process. The dielectric constant and leakage current of the films mere also strongly dependent on the postannealing conditions. BST thin film deposited on Ir bottom electrode at 500°C, after 700°C annealing in O₂ for 20 min, has the dielectric constant of 593, a loss tangent of 0.019 at 100 kHz, a leakage current density of 1.9×10 ^-8 A/cm² at an electric field of 200 kV/cm with a delay time of 30 s, and a charge storage density of 53 fC/μm² at an applied field of 100 kV/cm. The BST films deposited on Ir with post-annealing can obtain better dielectric properties than on other bottom electrodes in our experiments. And Ru electrode is unstable because the interdiffusion of Ru and Ti occurs at the interface between the BST and Ru after postannealing. The ten year lifetime of time-dependent dielectric breakdown (TDDB) studies indicate that BST on Pt, Ir, IrO₂/Ir, Ru, and RuO₂/Ru have long lifetimes over ten gears on operation at the voltage bias of 2 V     

Piezoresistive effect in GaAs/InxGa1−xAs/AlAs resonant tunneling diodes for application in micromechanical sensors

The current–voltage characteristics of GaAs/In_xGa_1−xAs/AlAs resonant tunneling diodes (RTDs) are a function of stress, and the current–voltage changes of RTDs with stress are attributed to the piezoresistive effect in RTDs. In order to study the piezoresistive effect in RTDs for application in micromachined mechanical sensors, the beam-mass structure based on RTDs is designed, fabricated and tested by the Wheatstone bridge test circuit. The test results show that the piezoresistive sensitivity of RTDs can be adjusted through the bias voltage, and the maximal piezoresistive sensitivity of RTDs with bias voltage at 0.618 V is 7.61×10⁻¹¹ Pa⁻¹, which is two orders higher than the minimal piezoresistive sensitivity (2.03×10⁻¹³ Pa⁻¹) of RTDs with bias voltage at 0.656 V, and is also higher than the piezoresistive sensitivity of silicon material (5.52×10⁻¹¹ Pa⁻¹).     

High temperature ohmic contacts to 3C–silicon carbide films

Currently, large-area 3C–SiC films are available from a number of sources and it is imperative that stable high temperature contacts be developed for high power devices on these films. By comparing the existing data in the literature, we demonstrate that the contact behavior on each of the different polytypes of SiC will vary significantly. In particular, we demonstrate this for 6H–SiC and 3C–SiC. The interface slope parameter, S, which is a measure of the Fermi-level pinning in each system varies between 0.4–0.5 on 6H–SiC, while it is 0.6 on 3C–SiC. This implies that the barrier heights of contacts to 3C–SiC will vary more significantly with the choice of metal than for 6H–SiC. Aluminum, nickel and tungsten were deposited on 3C–SiC films and their specific contact resistance measured using the circular TLM method. High temperature measurements (up to 400°C) were performed to determine the behavior of these contacts at operational temperatures. Aluminum was used primarily as a baseline for comparison since it melts at 660°C and cannot be used for very high temperature contacts. The specific contact resistance (ρ_c) for nickel at room temperature was 5×10⁻⁴ Ω cm², but increased with temperature to a value of 1.5×10⁻³ Ω cm² at 400°C. Tungsten had a higher room temperature ρ_c of 2×10⁻³ Ω cm², which remained relatively constant with increasing temperature up to 400°C. This is related to the fact that there is hardly any reaction between tungsten and silicon carbide even up to 900°C, whereas nickel almost completely reacts with SiC by that temperature. Contact resistance measurements were also performed on samples that were annealed at 500°C.     

High current bulk GaN Schottky rectifiers

GaN Schottky rectifiers employing guard-ring and SiO₂ edge termination show almost ideal forward current characteristics, with ideality factor 1.08 and specific on-state resistance as low as 2.6×10⁻³ Ω cm². A maximum forward current of 1.72 A at 6.28 V was achieved under pulsed (10% duty cycle) conditions. The reverse breakdown voltage was inversely dependent on rectifier area. The presence of defects in the GaN still dominates the reverse leakage, with both field emission and thermionic field emission contributions present. The parallel-plane breakdown voltage is never reached, even with the use of multiple edge termination methods, but the results show the promise of GaN rectifiers for power conditioning and electric utility applications.     

Electrical characteristics of high quality La2O3 gate dielectric with equivalent oxide thickness of 5 Å

Electrical and reliability properties of ultrathin La₂O ₃ gate dielectric have been investigated. The measured capacitance of 33 Å La₂O₃ gate dielectric is 7.2 μF/cm² that gives an effective K value of 27 and an equivalent oxide thickness of 4.8 Å. Good dielectric integrity is evidenced from the low leakage current density of 0.06 A/cm² at -1 V, high effective breakdown field of 13.5 MV/cm, low interface-trap density of 3×10¹⁰ eV^-1/cm², and excellent reliability with more than 10 years lifetime even at 2 V bias. In addition to high K, these dielectric properties are very close to conventional thermal SiO₂      

Low Weibull slope of breakdown distributions in high-k layers

The reliability of various Al₂O₃, ZrO₂ and Al₂O₃/ZrO₂ double layers with a physical oxide thickness from 3 nm to 15 nm and TiN gate electrodes was studied by measuring time-to-breakdown using gate injection and constant voltage stress. The extracted Weibull slope β of the breakdown distribution is found to be below 2 and shows no obvious thickness dependence. These findings deviate from previous results on intrinsic breakdown in SiO₂, where a strong thickness dependence was explained by the percolation model. Although promising performance on devices with high-k layers as dielectric can be obtained, it is argued that gate oxide reliability is likely limited by extrinsic factors     

Electrical properties of high permittivity ZrO2 gate dielectrics on strained-Si

Deposition and electrical properties of high dielectric constant (high-k) ultrathin ZrO₂ films on tensilely strained silicon (strained-Si) substrate are reported. ZrO₂ thin films have been deposited using a microwave plasma enhanced chemical vapor deposition technique at a low temperature (150 °C). Metal insulator semiconductor (MIS) structures are used for high frequency capacitance–voltage (C–V), current–voltage (I–V), and conductance–voltage (G–V) characterization. Using MIS capacitor structures, the reliability and the leakage current characteristics have been studied both at room and high temperature. Schottky conduction mechanism is found to dominate the current conduction at a high temperature. Observed good electrical and reliability properties suggest the suitability of deposited ZrO₂ thin films as an alternative as gate dielectrics. Compatibility of ZrO₂ as a gate dielectric on strained-Si is shown.     

Pt-based metallization of PMOS devices for a compatible monolithic integration of semiconducting/Yba2Cu3O7−δ superconducting devices on silicon

Mo, Pt, Pt/Mo and Pt/Ti thin films have been deposited onto Si and SiO₂ substrates by RF sputtering and annealed in the YBa₂Cu₃O_7−δ (YBCO) growth conditions. The effect of annealing on the sheet resistance of unpatterned layers was measured. A Pt-based multilayered metallization for the PMOS devices was proposed and tested for a compatible monolithic integration of semiconducting devices and YBCO sensors on the same silicon substrate. The best results were obtained with a Pt/Ti/Mo-silicide structure showing 0.472 Ω_□ interconnect sheet resistivity and 2×10⁻⁴ Ω cm² specific contact resistivity after annealing for 60 min at 700 °C in 0.5 mbar O₂ pressure.     

Design methodology and simulation tool for floating ring termination technique

A new methodology to optimize the design of floating ring (FR) termination technique for high voltage device is presented. The basic idea is to simulate the blocking capability of the structure with only one guard ring and then extend the results to a multiple FR system. A second advantage of our method is to include the ring width in the optimization process. The effectiveness and efficiency of our methodology is illustrated by optimizing a FR structure with a junction depth x_j=5 μm and Si substrate doping 2·10¹⁴ cm⁻³. A seven rings structure is optimized giving 85% efficiency in respect to the ideal plane parallel junction breakdown voltage V_BD=840 V. The simulation results are generated by the user-oriented simulation program POWER2D for studying the voltage handling capability of arbitrary shaped power semiconductor devices. A special algorithm is implemented ensuring very fast and automatic search of the breakdown via the ionization integrals calculus. An efficient numerical algorithm to drastically reduce the number of iterations when adjusting the quasi-Fermi potential of the floating rings has also been developped     

Studies of yttrium oxide films prepared by RF magnetron sputtering

Films of yttrium oxide (Y₂O₃) were deposited on Si substrates from a Y₂O₃ target by RF magnetron sputtering. MIS capacitors in the form of Al and Y₂O₃ (400 Å)-Si were then fabricated. The leakage current density was about 10^-6 A/cm² at 1.3×10⁶ V/cm, and the breakdown field of the films was about 2.75×10⁶ V/cm. The dielectric constant of the sputtered Y₂O₃ was found to be about 12-12.7     

GaN p–n junction diode formed by Si ion implantation into p-GaN

²⁸Si⁺ implantation into Mg-doped GaN, followed by thermal annealing in N₂ was performed to achieve n⁺-GaN layers. The carrier concentrations of the films changed from 3×10¹⁷ (p-type) to 5×10¹⁹ cm⁻³ (n-type) when the Si-implanted p-type GaN was properly annealed. Specific contact resistance (ρ_c) of Ti/Al/Pt/Au Ohmic contact to n-GaN, formed by ²⁸Si⁺ implantation into p-type GaN, was also evaluated by transmission line model. It was found that we could achieve a ρ_c value as low as 1.5×10⁻⁶ Ω cm² when the metal contact was alloyed in N₂ ambience at 600 °C. Si-implanted GaN p–n junction light-emitting diodes were also fabricated. Electroluminescence measurements showed that two emission peaks at around 385 and 420 nm were observed, which could be attributed to the near band-edge transition and donor-to-acceptor transition, respectively.     

Interface characteristics of Ge3N4-(n-type) GaAs MIS devices

Passivation of GaAs surfaces was achieved by the deposition of Ge₃N₄ dielectric films at low temperatures. Electrical characteristics of MIS devices were measured to determine the interface parameters. From C-V-f and G-V-f measurements, density of interface states has been obtained as (4–6)×10¹¹ cm⁻² eV⁻¹ at the semiconductor mid-gap. Some inversion charge buildup was seen in the C-V plot although the strong inversion regime is absent. Thermally stimulated current measurements indicate a trap density of 5×10¹⁸−10¹⁹ cm⁻³ in the dielectric film, with their energy level at 0.59 eV.