Effect of emitter contact on current gain of silicon bipolar devices

The common-emitter current gain β of silicon n-p-n bipolar transistors with shallow (200 nm) emitters contacted by either i) Al, ii) Pd2Si + Al, or iii) n⁺polysilicon + Al are compared. For the same base doping profile, β(Al) is typically about 25 percent larger than β(Pd2Si), while β(poly) is typically several times larger than β(Pd2Si). The dependence of the base current on temperature and on the thickness of the polysilicon layer indicates that the base current is not determined by the silicon-polysilicon interface properties, such as tunneling through an interfacial oxide layer, but by the transport of holes in the n⁺polysilicon layer. A simple two-region (n⁺silicon region and n⁺polysilicon region) model is presented which satisfactorily explains the experimental results in terms of lower hole mobility in the n⁺polysilicon than in the monocrystalline n⁺silicon.     

High-barrier Schottky diodes on p-type silicon due to dry-etching damage

It is known that the barrier height of Schottky diodes made to dry-etched silicon surfaces deviate from the barrier height values obtained for diodes fabricated on wet chemically etched or cleaved silicon. This effect, in cases where neither a substantial residue layer nor a surface film is formed, can be exploited to yield diodes on p-type Si that display barrier enhancement together with excellent diode ideality factors. It is shown that the barrier heights produced on p-type Si, by exploiting this effect of dry etching, can achieve a value of ∼0.75 eV which is ∼0.15 eV better than the best value reported for wet chemically etched or cleaved p-Si. When this barrier height value is attained, it is found to be independent of metallization. The same barrier height is achieved by two very different dry etching techniques: Ar⁺ion-beam etching (IBE) and CCl4reactive ion etching (RIE).     

High-barrier Al/p-Si Schottky diodes

Sequential implantation of argon ions and low-energy hydrogen ions has been found to yield Schottky barriers of exceptionally high values on p-type silicon. The interaction of these ions in Si is quite complex, involving donor defect generation, defect passivation, and acceptor dopant neutralization. The apparent synergism of these specific implants has resulted in Al/p-Si Schottky diodes with an effective barrier height as high as 0.83 eV, among the highest value reported for any metal/p-Si contact.     

Relationship between junction radius and reverse leakage of silicide Schottky-barrier diodes

Unguarded Schottky-barrier diodes exhibit excessive leakage current in the reverse-current direction. A portion of this excess current has always been attributed to sharp-edge effects. In this paper, the sharp-edge-related excess reverse current is attributed to the additional barrier lowering that is due to the electric-field enhancement present near the diode edges. Mathematical relationships describing the effect of the edge radius on the I-V characteristics of unguarded diodes are developed. These relationships are then used to model an unguarded Schottky-barrier diode. The correlation between the junction radius and the diode characteristics was found to be strong in the reverse-current direction. In the foward direction, the diode characteristics were not greatly affected, and thus the large diode-quality factors of unguarded diodes cannot be attributed to the sharp-edge effect. A comparison is made between the experimental characteristics of Pd2Si/ nSi and VSi2/nSi diodes and those obtained from modeling.     

Enhancement of effective barrier height in Ti-silicon Schottky diode using low-energy ion implantation

Increasing the effective barrier height in a Ti-p-type silicon Schottky diode has been achieved by means of low-energy ion implantation to introduce a thin inversion layer on silicon substrate. It is shown theoretically that effective barrier height equal to the energy bandgap can be obtained in such structure if the thickness and dopant density of the implanted layer are properly chosen. Experimental results for several titanium (Ti) on phosphorus implanted p-type silicon Schottky diodes show that effective barrier heights were increased from 0.6 eV for the Ti-p Si Schottky diode to 0.96 eV for a Ti-n-p-Si Schottky diode with a phosphorus-implanted layer thickness of 400 Å and dose of 1.26 × 10¹²cm^-2. Good agreement is obtained between the calculated and the measured barrier height for several Ti-n-p silicon Schottky diodes.     

Electrical characteristics of TiB2 for ULSI applications

The work function of TiB₂ was measured using Fowler-Nordheim tunneling in MOS capacitors, Schottky diode current measurements, capacitance-voltage techniques, and contact resistance. The resulting data place the Fermi level of TiB₂ about 0.9 eV below the silicon conduction band. Given this barrier height, Schottky diodes of TiB₂/p-Si exhibit ohmic characteristics, but the contact resistance of TiB₂ to n⁺ junctions is an order of magnitude higher than the generally desired value. Boron outdiffusion from TiB₂ into underlying silicon was observed at temperatures of 1000°C and greater. Boron diffusion from TiB₂ into silicon above 1000°C is enhanced compared to the conventionally accepted value of the boron diffusivity     

Optoelectronic properties of Zn0.52Se0.48/Si Schottky diodes

Zn_0.52Se_0.48/Si Schottky diodes are fabricated by depositing zinc selenide (Zn_0.52Se_0.48) thin films onto Si(1 0 0) substrates by vacuum evaporation technique. Rutherford backscattering spectrometry (RBS) analysis shows that the deposited films are nearly stoichiometric in nature. X-ray diffractogram of the films reveals the preferential orientation of the films along (1 1 1) direction. Structural parameters such as crystallite size (D), dislocation density (δ), strain (ε), and the lattice parameter are calculated as 29.13 nm, 1.187 × 10⁻¹⁵ lin/m², 1.354 × 10⁻³ lin⁻² m⁻⁴ and 5.676 × 10⁻¹⁰ m respectively. From the I–V measurements on the Zn_0.52Se_0.48/p-Si Schottky diodes, ideality and diode rectification factors are evaluated, as 1.749 (305 K) and 1.04 × 10⁴ (305 K) respectively. The built-in potential, effective carrier concentration (N_A) and barrier height were also evaluated from C–V measurement, which are found to be 1.02 V, 5.907 × 10¹⁵ cm⁻³ and 1.359 eV respectively.     

Silicon Schottky barriers and p-n junctions with highly stablealuminum contact metallization

Reactively sputtered amorphous Ta₃₆Si₁₄N₅₀ thin films are investigated as diffusion barriers to improve the thermal stability of contacts to electronic devices, specifically between Al overlayers and Si substrates. Electrical measurements on Schottky diodes and on shallow n ⁺-p junction diodes are used to evaluate the thermal stability of the (Si)/W₄₈Si₂₀N₃₂/Ta₃₆Si ₁₄N₅₀/Al metallization. The W₄₈Si₂₀N₃₂ contacting layer is added to raise the Schottky barrier height on n-type Si. It is shown that a 100-nm-thick Ta₃₆Si₁₄N₅₀ layer effectively prevents the intermixing between Al and Si. With this barrier layer, both shallow junctions and Schottky diodes are electrically stable up to 700°C for 20 min (above the Al melting point of 660°C ), which makes this material the best thin-film diffusion barrier on record     

Relating computer simulation studies with interface state measurements on MIS solar cells

A lock-in-amplifier technique has been used to measure interface state density (NSS) values ranging from 2 × 10¹¹-3 × 10¹³states/cm². eV depending on energy in the gap, type of Si substrate, and choice of Schottky metal used in MIS diodes. Polycrystalline, ribbon, and     

Formation of 0.05-μm p+-n and n+-pjunctions by very low (<500 eV) ion implantation

The current-voltage (I-V) characteristics of ultrashallow p⁺ -n and n⁺-p diodes, obtained using very-low-energy (<500-eV) implantation of B and As, are presented. the p⁺-n junctions were formed by implanting B⁺ ions into n-type Si (100) at 200 eV and at a dose of 6×10¹⁴ cm^-2, and n⁺-p junctions were obtained by implanting As⁺ ions into p-type (100) Si at 500 eV and at a dose 4×10¹² cm^-2. A rapid thermal annealing (RTA) of 800°C/10 s was performed before I-V measurements. Using secondary ion mass spectrometry (SIMS) on samples in-situ capped with a 20-nm ²⁸Si isotopic layer grown by a low-energy (40 eV) ion-beam deposition (IBD) technique, the depth profiles of these junctions were estimated to be 40 and 20 nm for p⁺-n and n⁺-p junctions, respectively. These are the shallowest junctions reported in the literature. The results show that these diodes exhibit excellent I-V characteristics, with ideality factor of 1.1 and a reverse bias leakage current at -6 V of 8×10^-12 and 2×10^-11 A for p⁺-n and n⁺-p diodes, respectively, using a junction area of 1.96×10^-3 cm²     

Pt-Ir silicide Schottky-barrier IR detectors

Schottky-barrier infrared detectors have been fabricated with silicide electrodes formed by sequential vacuum deposition of 5-10-Å-thick Pt and 10-20-Å-thick Ir layers on p-type Si substrates and subsequent thermal annealing. The barrier heights of the Pt-Ir Schottky diodes are 0.16-0.9 eV, compared with 0.22 eV for Pt-only diodes, and the detector cutoff wavelengths extend well beyond 6 μm. Furthermore, the Pt-Ir diodes exhibit higher detector quantum efficiency than either Pt-only or Ir-only diodes over a significant spectral range     

A High Schottky-Barrier of 1.1 eV Between Al and S-Passivated p-Type Si(100) Surface

We report a high Schottky-barrier between Al and S-passivated p-type Si(100) surface. Capacitance-voltage measurements indicate a barrier height of 1.1 eV, while activation-energy measurements suggest 0.94-0.97 eV. Possible reasons for the discrepancy are proposed. The barrier height of 1.1 eV suggests degenerate inversion on the p-type Si surface, and Fermi statistics is used to describe its electrostatics. Although fabricated like a Schottky diode, this Al/S-passivated p-type Si(100) device works like a p-n junction diode. Temperature-dependent current-voltage measurements reveal that S passivation reduces the reverse saturation current of Al/p-type Si(100) diodes by over six orders of magnitude     

用弹道电子发射显微术研究超薄金属硅化物/硅肖特基接触

采用弹道电子发射显微术 ( BEEM)技术对超薄 Pt Si/Si、Co Si2 /Si肖特基接触特性进行了研究 ,并与电流 -电压 ( I- V)及电容 -电压 ( C- V)测试结果进行了对比 .研究了 Ar离子轰击对超薄Pt Si/n- Si肖特基接触特性的影响 .BEEM、I- V/C- V技术对多种样品的研究结果表明 ,I- V/C- V测试会由于超薄硅化物层串联电阻的影响而使测试结果产生严重误差 ;BEEM测试则不受影响 .随着离子轰击能量增大 ,肖特基势垒高度降低 ,且其不均匀性也越大 .用 BEEM和变温 I- V对超薄 Co Si2 /n- Si肖特基二极管的研究结果表明 ,变温 I- V测试可在一定程度上获得肖特基势垒     

IrSi Schottky-barrier infrared detectors with wavelength responsebeyond 12 μm

Schottky-barrier infrared detectors with a 4-nm-thick IrSi electrode have been fabricated on p-Si substrates previously implanted with low-energy boron ions. Low-energy boron ion implantation has been used to form a shallow p⁺-Si layer that lowers the barrier height of IrSi-Si Schottky-barrier contacts by the image-force effect and field-assisted tunneling. IrSi infrared detectors with a cutoff wavelength beyond 12 μm have been obtained by this technique. The optical barrier height found by spectral response measurements is 0.100 eV, which corresponds to a detector cutoff wavelength of 12.4 μm     

High-power high-reliability operation of 1.3 µm p-substrate buried crescent laser diodes

Stable high-power CW operation of 1.3-μm InGaAsP/InP p-substrate buried crescent laser diodes (PBC-LD'S) has been realized, by controlling the front and rear facet reflectivities of the laser diode chips. The front facet reflectivity is reduced to 17 percent and the rear facet reflectivity is increased to 90 percent, by evaporating multilayer dielectric films (Si/Al2O3SiO2:17 percent, SiO2/Si/SiO2/Si/SiO2:90 percent) on each facet. CW light output power of 50 mW is achieved up to 60°C. Aging tests have been carried out under automatic power control (APC) mode conditions of 50°C-30 mW, 40 mW, 50 mW, and 30°C-50 mW. All samples are operating stably in spite of junction-up configuration. The lifetimes are estimated to be more than2 times 10^{4}h for all conditions.     

Improved Ni Schottky Contacts on <Emphasis Type="Italic">n</Emphasis>-Type 4H-SiC Using Thermal Processing

High-temperature processing was used to improve the barrier properties of three sets of n-type 4H-SiC Schottky diodes fabricated with Ni Schottky contacts. We obtained an optimum average barrier height of 1.78 eV and an ideality factor of 1.09 using current–voltage measurements on diodes annealed in vacuum at 500°C for 24 h. Nonannealed contacts had an average barrier height of 1.48 eV and an ideality factor of 1.85. The Rutherford backscattering spectra of the Ni/SiC contacts revealed the formation of a nickel silicide at the interface, accompanied by a substantial reduction in oxygen following annealing.     

High-Quality Schottky Contacts for Limiting Leakage Currents in Ge-Based Schottky Barrier MOSFETs

Schottky barrier (SB) Ge channel MOSFETs suffer from high drain-body leakage at the required elevated substrate doping concentrations to suppress source–drain leakage. Here, we show that electrodeposited Ni–Ge and NiGe/Ge Schottky diodes on highly doped Ge show low off current, which might make them suitable for SB p-MOSFETs. The Schottky diodes showed rectification of up to five orders of magnitude. At low forward biases, the overlap of the forward current density curves for the as-deposited Ni/n-Ge and NiGe/n-Ge Schottky diodes indicates Fermi-level pinning in the Ge bandgap. The SB height for electrons remains virtually constant at 0.52 eV (indicating a hole barrier height of 0.14 eV) under various annealing temperatures. The series resistance decreases with increasing annealing temperature in agreement with four-point probe measurements indicating the lower specific resistance of NiGe as compared to Ni, which is crucial for high drive current in SB p-MOSFETs. We show by numerical simulation that by incorporating such high-quality Schottky diodes in the source/drain of a Ge channel PMOS, a highly doped substrate could be used to minimize the source-to-drain subthreshold leakage current.      

Schottky Barrier Height of Erbium Silicide on $ hbox{Si}_{1 - x}hbox{C}_{x}$

In this letter, the Schottky barrier height of erbium silicide contacts formed on $hbox{Si}_{1 - x}hbox{C}_{x}$ alloys was measured. The alloys were pseudomorphically grown on Si wafers with 0% to 1.2% C occupying the substitutional sites. Schottky barrier diodes were fabricated with an ideality factor of 1.13 or less. The hole barrier height was found to be 0.73 eV independent of the C concentration. This suggests that the electron barrier height should decrease with increasing C concentration due to the reduction in the semiconductor bandgap. For 1.2% C, the electron barrier is estimated to be 0.29 eV.      

Fabrication and performance of GaAs p+n junction and Schottky barrier millimeter IMPATT's

A recently developed procedure, incorporating both preferential electrochemical etching for wafer thinning and electroplating for heat sink formation has been applied to the fabrication of Kaband (26.5-40 GHz) GaAs IMPATT's. Both epitaxially grown GaAs p⁺n junction and Cr Schottky barrier diodes have been fabricated. This procedure makes possible the batch fabrication of small area diodes (<2 times 10^{-5}cm²) over a large wafer area. The diodes have been operated both in the oscillator and stable-amplifier mode. Power, efficiency, and noise performance of the devices is reported. The p⁺n diodes, which could withstand junction temperature of over 300°C, gave the best power and efficiency. Powers as high as 680 mW with 12.4 percent efficiency at 34.8 GHz and an efficiency as high as 16 percent with 390 mW at 29.5 GHz have been achieved. The Cr Schottky diodes were unable to withstand junction temperatures in excess of 200°C and therefore produced less power despite the potentially better power handling capability. The highest power obtained from a Cr Schottky is 470 mW with 12.5 percent efficiency at 34 GHz. Comparable oscillator noise performance has been obtained with both types of diode. The best AM (DSB) double sideband NSR obtained is -135 dB in a 100 Hz window at 1.5 MHz from the carrier. An rms frequency deviation as low as 13 Hz in a 100 Hz window has been observed with a power output of 164 mW at 35.4 GHz by raising the external Q to 138. A lowest FM noise measure of 23 dB was achieved by reducing output power to 16 mW. The amplifier noise figure measured for both p⁺n and Cr Schottky diodes is 26 dB.     

High voltage 4H-SiC Schottky barrier diodes

Characteristics of 4H-SiC Schottky barrier diodes with breakdown voltages up to 1000 V are reported for the first time. The diodes showed excellent forward I-V characteristics, with a forward voltage drop of 1.06 V at an on-state current density of 100 A/cm². The specific on-resistance for these diodes was found to be low (2×10 ^-3 Ω-cm² at room temperature) and showed a T ^1.6 variation with temperature. Titanium Schottky barrier height was determined to be 0.99 eV independent of the temperature. The breakdown voltage of the diodes was found to decrease with temperature