Improved uniformity of contact resistance in GaAs MESFET usingPd/Ge/Ti/Au ohmic contacts

Improved contact resistance uniformity, with a low resistance on high-low doped GaAs MESFET, was demonstrated using a Pd/Ge/Ti/Au ohmic contact. The lowest contact resistivity obtained was 2.8×10^-6 Ω-cm². The average value and standard deviation (ΔRc) of the contact resistance (Rc) were 0.73 and 0.07 Ω-mm, respectively, which were more uniform than those for AuGe/Ni contacts with an average Rc of 0.77 Ω-mm and ΔRc of 0.16 Ω-mm. The improved uniformity was attributed to the uniform penetration of the ohmic junction into the buried high-doped channel layer by solid-state reactions, resulting in the improved uniformity of device performance     

Electrical characterization of annealed Ti/TiN/Pt contacts onN-type 6H-SiC epilayer

We report results of the electrical characteristics of in vacuo deposited Ti/TiN/Pt contact metallization on n-type 6H-SiC epilayer as function of impurity concentration in the range of 3.3×10¹⁷ cm^-3 to 1.9×10¹⁹ cm^-3. The as-deposited contacts are rectifying, except for the highly doped sample. Only the lesser doped remains rectifying after samples are annealed at 1000°C between 0.5 and 1 min in argon. Bulk contact resistance ranging from factors of 10^-5 to 10^-4 Ω-cm² and Schottky barrier height in the range of 0.54-0.84 eV are obtained. Adhesion problems associated with metal deposition on pre-processed titanium is not observed, leading to excellent mechanical stability. Auger electron spectroscopy (AES) reveals the out diffusion of Ti-Si and agglomeration of Ti-C species at the epilayer surface. The contact resistance remains appreciably stable after treatment in air at 650°C for 65 h. The drop in SBH and the resulting stable contact resistance is proposed to be associated with the thermal activation of TiC diffusion barrier layer on the 6H-SiC epilayer during annealing     

Schottky barrier height of a new ohmic contact NiSi2 to n-type 6H-SiC

We present a new ohmic contact material NiSi₂ to n-type 6H-SiC with a low specific contact resistance. NiSi₂ films are prepared by annealing the Ni and Si films separately deposited on (0 0 0 1)-oriented 6H-SiC substrates with carrier concentrations (n) ranging from 5.8×10¹⁶ to 2.5×10¹⁹ cm⁻³. The deposited films are annealed at 900 °C for 10 min in a flow of Ar gas containing 5 vol.% H₂ gas. The specific contact resistance of NiSi₂ contact exponentially decreases with increasing carrier concentrations of substrates. NiSi₂ contacts formed on the substrates with n=2.5×10¹⁹ cm⁻³ show a relatively low specific contact resistance with 3.6×10⁻⁶ Ω cm². Schottky barrier height of NiSi₂ to n-type 6H-SiC is estimated to be 0.40±0.02 eV using a theoretical relationship for the carrier concentration dependence of the specific contact resistance.     

Low-operation voltage of InGaN-GaN light-emitting diodes withSi-doped In0.3Ga0.7N/GaN short-period superlatticetunneling contact layer

InGaN/GaN multiple-quantum-well light-emitting diode (LED) structures including a Si-doped In_0.23Ga_0.77N/GaN short-period superlattice (SPS) tunneling contact were grown by metalorganic vapor phase epitaxy. In_0.23Ga_0.77N/GaN(n⁺)-GaN(p) tunneling junction, the low-resistivity n⁺-In_0.3Ga_0.77 N/GaN SPS instead of high-resistivity p-type GaN as a top contact layer, allows the reverse-biased tunnel junction to form an “ohmic” contact. In this structure, the sheet electron concentration of Si-doped In_0.23Ga_0.77N/GaN SPS is around 1×10¹⁴/cm², leading to an averaged electron concentration of around 1×10²⁰/cm³. This high-conductivity SPS would lead to a low-resistivity ohmic contact (Au/Ni/SPS) of LED. Experimental results indicate that the LEDs can achieve a lower operation voltage of around 2.95 V, i.e., smaller than conventional devices which have an operation voltage of about 3.8 V     

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.     

Contacts on GalnAs

The specific contact resistance ρcof Ni/Au-Ge/Ni and Ni/Au-Sn/Ni layers on n-GaInAs and Ni/Au-Mg/Ni and Ni/Au-Zu/Ni on p-GaInAs are measured for different alloying temperatures and times using an extended transmission line model. Specific contact resistances of 4.10^-8Ω cm²for Ni/Au-Sn/Ni on n-GaInAs (n = 10¹⁸cm^-3) and 2.10^-5Ω. cm²for Ni/Au-Zn/Ni on p-GaInAs (p = 10¹⁸cm^-3) are obtained. After deposition at room temperature, the barrier height of the metal-n-GaInAs system was determined to be 0.16 eV, decreasing below 20 meV after heat treatment. Interdiffusion of metal and semiconductor was investigated by SIMS/Auger measurements. At alloying temperature of 300°C the contacts show fast diffusion of Au relative to the dopants, effecting an increase of the specific contact resistance.     

Laser annealed Ta/Ge and Ni/Ge ohmic contacts to GaAs

Refractory metal ohmic contacts to n-type GaAs have been developed using epitaxial Ge films and pulsed laser annealing. Laser annealing was carried out with a 22 ns pulse from a Q-switched ruby laser operating in the TEM00mode. The specific contact resistivity of the contacts Ta/Ge and Ni/Ge on 2 × 10¹⁷cm^-3dopes GaAs exhibited sharp minima as a function of laser energy density at 1 × 10^-6Ω-cm²and 2 × 10^-6Ω-cm², respectively, which occurred near the melting point of the layered contacts. Auger electron sputter profiles revealed Ge migration into the GaAs surface after laser annealing at sufficient energy density to form ohmic contact. The contacts have applications to high temperature devices and to devices which experience high channel or contact temperatures, such as power FETs and TEDs.     

Al/W/TiNx/TiSiy/Si barrier technology for1.0-μm contacts

A reliable contact diffusion barrier has been successfully formed by sintering in nitrogen a physically sputtered W/Ti bilayer. After a 650°C furnace anneal, a TiN_x/TiSi_y layer on contact with the silicon substrate was formed beneath the overlying W. No reaction between N₂ and W was observed. Arsenic implanted in the silicon substrate tended to retard the silicidation of titanium. Substantial redistribution of both B and As across the silicide layer was also observed during the contact sintering process. The 1.0-μ contacts fabricated with the Al/W/TiN_x/TiSi_y/Si barrier technology exhibited low and tightly distributed contact resistivities (less than 10^-6 Ω-cm²). No excessive leakage of the shallow junctions was observed even after thermally stressing the sample at 400°C for 8 h     

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.     

High performance of high-voltage 4H-SiC Schottky barrier diodes

High performance of high-voltage rectifiers could be realized utilizing 4H-SiC Schottky barrier diodes. A typical specific on-resistance (R_on) of these devices was 1.4×10³ Ω cm³ at 24°C (room temperature) with breakdown voltages as high as 800 V. These devices based on 4H-SiC had R _on's lower than 6H-SiC based high-power rectifiers with the same breakdown voltage. As for Schottky contact metals, Au, Ni, and Ti were employed in this study. The barrier heights of these metals for 4H-SiC were determined by the analysis of current-voltage characteristics, and the reduction of power loss could be achieved by controlling the barrier heights     

Low emitter resistance GaAs based HBT's without InGaAs caps

Low emitter resistance is demonstrated for AlGaAs/GaAs heterojunction bipolar transistors using Pd/Ge contacts on a GaAs contact layer. The contact resistivity to 2-10×10¹⁸ cm ^-3 n-type GaAs is 4-1×10^-7 Ω-cm² . These are comparable to contact resistivities obtained with non-alloyed contacts on InGaAs layers. The non-spiking Pd/Ge contact demonstrates thermal stability and area independent resistivity suitable for scaled devices. The substitution of Pd/Ge for AuGe/Ni GaAs emitter and collector contacts reduced by an order of magnitude the emitter-base offset voltage at high current densities and increased f_t by more than 15% with significantly improved uniformity for devices with 2 and 2.6 μm wide emitters having lengths two, four and six times the width     

Solid-phase epitaxial Pd/Ge ohmic contacts to In1-xGaxAsyP1-y/InP

A Pd/Ge metallization to InGaAsP/InP semiconductors, formed with solid-phase epitaxy (SPE) technique, has been investigated in this study. With this method, ohmic contacts with low specific contact resistance (rho_{c} approx 2.3 times 10^{-6}Ω.cm²) have been achieved on p-type In0.53Ga0.47As(p approx 1.8 times 10^{19}/cm³). The same contact scheme also gives low specific contact resistance (rho_{c} approx 6 times 10^{-7}Ω.cm²) on n-type In0.53Ga0.47As (n approx 1.0 times 10^{19}/cm³). Excellent surface morphology is observed in all the samples, and the contacts do not deteriorate for at least 4 h at temperatures between 300 and 500°C.     

Ti/Al/Ni/Au金属体系在N-polar GaN上的欧姆接触特性

利用金属有机化合物化学气相淀积(MOCVD)在SiC衬底上外延生长了N-polar GaN材料,采用传输线模型(TLM)分析了Ti/Al/Ni/Au金属体系在N-polar GaN上的欧姆接触特性.结果表明,Ti/Al/Ni/Au (20/60/10/50 nm)在N-polar GaN上可形成比接触电阻率为2.2×10-3Ω·cm2的非合金欧姆接触,当退火温度升至200℃,比接触电阻率降为1.44×10-3 Ω·cm2,随着退火温度的进一步上升,Ga原子外逸导致欧姆接触退化为肖特基接触.     

Ohmic contacts on diamond by B ion implantation and Ti-Aumetallization

Low-resistance ohmic contacts have been fabricated on a natural IIb semiconducting diamond crystal and on undoped polycrystalline diamond films by B ion implantation and subsequent metallization with a Ti-Au bilayer metallization. A high B concentration of ~7×10²⁰ cm^-3 at the surface was obtained by ion implantation, a post-implant anneal, and a subsequent chemical removal of the graphite layer that resulted from the radiation damage. A bilayer metallization of Ti followed by Au annealed at 850°C yielded a specific contact resistance value on the order of 10^-6 Ω-cm² for chemical-vapor-deposition-grown polycrystalline films and on the order of 10^-5 Ω-cm² for the semiconducting natural crystal     

LaNiO3: a promising material for contact with YBa2Cu3O7-x thin films

Epitaxial LaNiO₃ metallic oxide thin films have been grown on c-axis oriented YBa₂Cu₃O_7-δ thin films on LaAlO₃ substrates by pulsed laser deposition technique and the interface formed between the two films has been examined by measuring the contact conductance of the same. The specific contact conductance of the interface measured using a modified four probe method was found to be 1.4 to 6×10⁴ ohm^-1 cm^-2 at 77 K. There are indications that contact conductance can be brought closer to that obtained for noble metal-YBCO interface     

Nickel ohmic contacts to p and n-type 4H-SiC

The first demonstration of Ni ohmic contacts to both p⁺ and n⁺ 4H-SiC formed by ion implantation is reported. Sample preparation conditions are described and experimental results presented. Specific contact resistances in the range of 10^-4 Ω cm ² and 10^-6 Ω cm² for p⁺ and n⁺ 4H-SiC, respectively, have been determined by the transfer length method     

Low-resistance bandgap-engineeredW/Si1-xGex/Si contacts

Bandgap-engineered W/Si_1-xGe_x/Si junctions (p⁺ and n⁺) with ultra-low contact resistivity and low leakage have been fabricated and characterized. The junctions are formed via outdiffusion from a selectively deposited Si_0.7Ge _0.3 layer which is implanted and annealed using RTA. The Si _1-xGe_x layer can then be selectively thinned using NH₄OH/H₂O₂/H₂O at 75°C with little change in characteristics or left as-deposited. Leakage currents were better than 1.6×10^-9 A/cm² (areal), 7.45×10^-12 A/cm (peripheral) for p⁺/n and 3.5×10^-10 A/cm² (peripheral) for n⁺/p. W contacts were formed using selective LPCVD on Si_1-xGe_x. A specific contact resistivity of better than 3.2×10^-8 Ω cm² for p ⁺/n and 2.2×10^-8 Ω cm² for n⁺/p is demonstrated-an order of magnitude n⁺ better than current TiSi₂ technology. W/Si_1-xGe _x/Si junctions show great potential for ULSI applications     

InP/InGaAs HBTs with n+-InP contacting layers grown byMOMBE using SiBr4

InP/InGaAs heterojunction bipolar transistors (HBTs) with low resistance, nonalloyed TiPtAu contacts on n⁺-InP emitter and collector contacting layers have been demonstrated with excellent DC characteristics. A specific contact resistance of 5.42×10^-8 Ω·cm², which, to the best of our knowledge, is the lowest reported for TiPtAu on n-InP, has been measured on InP doped n=6.0×10¹⁹ cm^-3 using SiBr₄. This low contact resistance makes TiPtAu contacts on n-InP viable for InP/InGaAs HBTs     

In0.52Al0.48As/In0.53Ga0.47As double-heterojunction p-n-p bipolar transistors grown bymolecular beam epitaxy

P-n-p In_0.52Al_0.48As/In_0.53Ga_0.47 As double-heterojunction bipolar transistors with a p⁺-InAs emitter cap layer grown by molecular-beam epitaxy have been realized and tested. A five-period 15-Å-thick In_0.53Ga_0.47As/InAs superlattice was incorporated between the In_0.53Ga_0.47As and InAs cap layer to smooth out the valence-band discontinuity. Specific contact resistance of 1×10^-5 and 2×10^-6 Ω-cm² were measured for nonalloyed emitter and base contacts, respectively. A maximum common emitter current gain of 70 has been measured for a 1500-Å-thick base transistor at a collector current density of 1.2×10³ A/cm². Typical current gains of devices with 50×50-μm² emitter areas were around 50 with ideality factors of 1.4     

Thermally Stable Mirror Structures for Vertical-Conducting GaN/Mirror/Si Light-Emitting Diodes

Vertical-conducting GaN/mirror/Si light-emitting diodes (LEDs) with thermally stable mirrors have been fabricated using a combination of wafer-bonding and laser liftoff techniques. The thermal stabilities of NiO-Ag, NiO-Ag-Ni, and NiO-Au-Ag mirrors and their effects on the performance of mirror-substrate LEDs were studied. It is found that the NiO-Ag-Ni mirror presents the best performance, where the specific contact resistance and the reflectivity can achieve 5.1times10^-3 Omega-cm² and 92% at 470 nm after oxidation annealing at 500degC for 10 min. The top Ni layer could protect the Ag mirror from clustering during the thermal treatment process. The output powers of the GaN-sapphire and GaN/mirror/Si LEDs with NiO-Au-Ag and NiO-Ag-Ni mirrors show 4.5, 4.3, and 13 mW, respectively.