Improved Schottky barrier on n-Sb/sub 2/S/sub 3/ films chemically deposited with silicotungstic acid (solar cells)

The first fabrication of low cost Schottky barrier solar cells on chemically deposited polycrystalline n-Sb/sub 2/S/sub 3/ thin films is reported. It is observed that in the films deposited with silicotungstic acid and annealed, the Schottky barrier height ( phi /sub b/) of the Au/n-Sb/sub 2/S/sub 3/ junctions is considerably improved from 0.54 to 0.76 eV. The ideality factor n decreased from 2.32 to 1.08 and the reverse-saturation current density J/sub 0/ from 3.2*10/sup -6/ to 1.5*10/sup -9/ A cm/sup -2/. Under AM1 illumination, the improved diode exhibited a conversion efficiency of approximately 3%.<>     

A new, high-voltage 4H-SiC lateral dual sidewall Schottky (LDSS) rectifier: theoretical investigation and analysis

In this paper, we report a new 4 H-silicon carbide (SiC) lateral dual sidewall Schottky (LDSS) rectifier on a highly doped drift layer consisting of a high-barrier sidewall Schottky contact on top of the low-barrier Schottky contact. Using two-dimensional (2-D) device simulation, the performance of the proposed device has been evaluated in detail by comparing its characteristics with those of the compatible lateral conventional Schottky (LCS) and lateral trench sidewall Schottky (LTSS) rectifiers on 4H-SiC. From our simulation results, it is observed that the proposed LDSS rectifier acts as a low-barrier LTSS rectifier under forward-bias conditions, and as a high-barrier LTSS rectifier under reverse-bias conditions, making it an ideal rectifier. The LDSS rectifier exhibits an on/off current ratio (at 1 V/-500 V) of 5.5/spl times/10/sup 7/ for an epitaxial layer doping of 1/spl times/10/sup 17/ /cm/sup 3/. Further, the proposed LDSS structure exhibits a very sharp breakdown similar to that of a p-i-n diode in spite of using only Schottky junctions in the structure. We have analyzed the reasons for the improved performance of the LDSS.     

GaAs Integrated Microwave Circuits

GaAs has many desirable features that make it most useful for microwave and millimeter-wave integrated circuits.The process of selective epitaxial depositions of high purity single-crystal GaAs with various doping concentrations into semi-insulating GaAs substrates has been developed. These high-resistivity substrates (> 10 /sup 6/ ohm cm) provide the electrical isolation between devices, eliminating the difficulties and deficiencies normally encountered in trying to obtain isolation with dielectrics, back-etching, p-n junctions, etc. This monolithic approach to integrated circuits thus allows for improved microwave performance from the devices since parasitics are reduced to a minimum. Planar Gunn oscillators and Schottky barrier diodes have been fabricated for use in a completely monolithic integrated millimeter wave (94GHz) receiving front end.The Gunn oscillators are made in a sandwich-type structure of three selective deposits whose carrier concentrations are approximately 10 /sup 18/ -10 /sup 15/ -10 /sup 18/ cm /sup -3/.The Schottky diodes consist of two deposits with concentrations of 10 /sup 18/ and 10 /sup 17/ cm /sup -3/.The Schottky contact is formed by evaporating Mo-Au onto the 10 /sup 17/ cm /sup -3/ deposits; all ohmic contacts are on the surface and are alloyed to the N+ regions.     

GaAs Integrated Microwave Circuits

GaAs has many desirable features that make it most useful for microwave and millimeter-wave integrated circuits. The process of selective epitaxial depositions of high purity single-crystal GaAs with various doping concentrations into semi-insulating GaAs substrates has been developed. These high-resistivity substrates (>10/sup 6/ ohm /spl dot/ cm) provide the electrical isolation between devices, eliminating the difficulties and deficiencies normally encountered in trying to obtain isolation with dielectrics, back-etching, p-n junctions, etc. This monolithic approach to integrated circuits thus allows for improved microwave performance from the devices since parasitic are reduced to a minimum. Planar Gunn oscillators and Schottky barrier diodes have been fabricated for use in a completely monolithic integrated millimeter wave (94 GHz) receiving front end. The Gunn oscillators are made in a sandwich-type structure of three selective deposits whose carrier concentrations are approximately 10/sup 18/ - 10/sup/15/ - 10/sup 18/ cm/sup -3/. The Schottky diodes consist of two deposits with concentrations of 10/sup 18/ and 10/sup 17/ cm /sup -3/. The Schottky contact is formed by evaporating Mo-Au onto the 10/sup 17/cm/sup -3/ deposits; all ohmic contacts are on the surface and are alloyed to the N/sup +/ regions.     

N-type Schottky barrier source/drain MOSFET using ytterbium silicide

Ytterbium silicide, for the first time, was used to form the Schottky barrier source/drain (S/D) of N-channel MOSFETs. The device fabrication was performed at low temperature, which is highly preferred in the establishment of Schottky barrier S/D transistor (SSDT) technology, including the HfO/sub 2/ gate dielectric, and HaN/TaN metal gate. The YbSi/sub 2 - x/ silicided N-SSDT has demonstrated a very promising characteristic with a recorded high I/sub on//l/sub off/ ratio of /spl sim/10/sup 7/ and a steep subthreshold slope of 75 mV/dec, which is attributed to the lower electron barrier height and better film morphology of the YbSi/sub 2 - x//Si contact compared with other self-aligned rare earth metal-(Erbium, Terbium, Dysprosium) silicided Schottky junctions.     

Influence of surface defect charge at AlGaN-GaN-HEMT upon Schottky gate leakage current and breakdown voltage

The relation between Schottky gate leakage current and the breakdown voltage of AlGaN-GaN high-electron mobility transistors (HEMTs) is discussed based on the newly introduced simple, yet useful, surface defect charge model. This model represents the leakage current caused by the positive charge in the surface portion of AlGaN layer induced by process damage such as nitrogen vacancies. The new model has been implemented into a two-dimensional device simulator, and the relationship between the gate leakage current and the breakdown voltage was simulated. The simulation results reproduced the relationship obtained experimentally between the leakage current and the breakdown voltage. Further simulation and experiment results show that the breakdown voltage is maintained even if the defect charge exists up to the defect charge density of 2.5/spl times/10/sup 12/ cm/sup -2/, provided the field plate structure is adopted, while the breakdown voltage shows a sudden drop for the defect density over 5/spl times/10/sup 11/ cm/sup -2/ without the field plate. This result shows that the field plate structure is effective for suppressing the surface charge influence on breakdown voltage due to the relaxation of the electric field concentration in the surface portion of the AlGaN layer.     

Formation of Ni germano-silicide on single crystalline Si/sub 0.3/Ge/sub 0.7//Si

We have studied the Ni and Co germano-silicide on Si/sub 0.3/Ge/sub 0.7//Si. The Ni germano-silicide shows a low sheet resistance of 4-6 /spl Omega///spl square/on both P/sup +/N and N/sup +/P junctions, which is much smaller than Co germano-silicide. In addition, small junction leakage currents of 3/spl times/10/sup -8/ A/cm/sup 2/ and 2/spl times/10/sup -7/ A/cm/sup 2/ are obtained for Ni germano-silicide on P/sup +/N and N/sup +/P junctions, respectively. The good germano-silicide integrity is due to the relatively uniform thickness as observed by cross-sectional TEM.     

Demonstration of the first 10-kV 4H-SiC Schottky barrier diodes

This letter reports the demonstration of the first 4H-SiC Schottky barrier diode (SBD) blocking over 10 kV based on 115-/spl mu/m n-type epilayers doped to 5.6 /spl times/ 10/sup 14/ cm/sup -3/ through the use of a multistep junction termination extension. The blocking voltage substantially surpasses the former 4H-SiC SBD record of 4.9 kV. A current density of 48 A/cm/sup 2/ is achieved with a forward voltage drop of 6 V. The Schottky barrier height, ideality factor, and electron mobility for this very thick epilayer are reported. The SBD's specific-on resistance is also reported.     

Optimization of large band-gap barriers for reducing leakage in bipolar cascade lasers

In order to study the characteristics of bipolar cascade lasers, we have developed a fully consistent transport model compatible with Esaki tunnel junctions (TJs). First, we compare the calculated electrical characteristics of TJs made of different InGaAsP lattice-matched to InP materials with different doping concentrations. Then, a complex (p-n)-(n/sup ++/p/sup ++/)-(p-n)-(n/sup ++/p/sup ++/)-p-n) structure is implemented. The Esaki junctions are cladded by doped InP current confining layers, the width of which is optimized to prevent electron leakage. We find that a 25-nm-wide InP barrier confines more than 98% of the electron current for a total injection current of 10 kA.cm/sup -2/ at room temperature. The predicted differential quantum efficiency is then 230%.     

InAlN/GaN HEMTs: a first insight into technological optimization

High-electron mobility transistors (HEMTs) were fabricated from heterostructures consisting of undoped In/sub 0.2/Al/sub 0.8/N barrier and GaN channel layers grown by metal-organic vapor phase epitaxy on (0001) sapphire substrates. The polarization-induced two-dimensional electron gas (2DEG) density and mobility at the In/sub 0.2/Al/sub 0.8/N/GaN heterojunction were 2/spl times/10/sup 13/ cm/sup -2/ and 260 cm/sup 2/V/sup -1/s/sup -1/, respectively. A tradeoff was determined for the annealing temperature of Ti/Al/Ni/Au ohmic contacts in order to achieve a low contact resistance (/spl rho//sub C/=2.4/spl times/10/sup -5/ /spl Omega//spl middot/cm/sup 2/) without degradation of the channels sheet resistance. Schottky barrier heights were 0.63 and 0.84 eV for Ni- and Pt-based contacts, respectively. The obtained dc parameters of 1-/spl mu/m gate-length HEMT were 0.64 A/mm drain current at V/sub GS/=3 V and 122 mS/mm transconductance, respectively. An HEMT analytical model was used to identify the effects of various material and device parameters on the InAlN/GaN HEMT performance. It is concluded that the increase in the channel mobility is urgently needed in order to benefit from the high 2DEG density.     

Ultraviolet laser-assisted surface treatment of InP with phosphine gas

InP surface has been treated with phosphine (PH₃) gas photodecomposed by ArF excimer laser at a temperature as low as 150° C. It is shown by Auger electron spectroscopy analysis that the photolytic process of PH₃ gas is capable of removing native oxide and depositing simultaneously amorphous P film on the InP surface. Moreover, hydrogenation occurs on and near the surface of InP. An enhancement of the barrier height up to 0.63 eV is demonstrated for MIS Schottky junctions with a thin P layer formed on the treated InP substrates. Furthermore, it is shown that the barrier height varies depending on work function of the Schottky metal on the treated InP. This suggests that the present process causes a reduction in the surface state density which permits weakening of the Fermi level pinning at the surface of InP.     

Surface Transport Phenomena in Pb/p-PbSe Junctions

Pb/p-PbSe junctions have been formed on Si (111) substrates. The p-PbSe thin film was grown by Molecular Beam Epitaxy (MBE). A qualitative study of the effect of surface defects in the region between the Schottky and ohmic contact is made through a comparison of parameters as the sheet resistance and the saturation current density.     

Highly reliable GaN-based light-emitting diodes formed by p-In/sub 0.1/Ga/sub 0.9/N-ITO structure

Indium-tin-oxide (ITO) is deposited as a transparent current spreading layer of GaN-based light-emitting diodes (LEDs). To reduce the interfacial Schottky barrier height, a thin p-In/sub 0.1/Ga/sub 0.9/N layer is grown as an intermediate between ITO and p-GaN. The contact resistivity around 2.6/spl times/10/sup -2/ /spl Omega//spl middot/cm/sup 2/ results in a moderately high forward voltage LED of 3.43 V operated at 20 mA. However, the external quantum efficiency and power efficiency are enhanced by 46% and 36%, respectively, in comparison with the conventional Ni-Au contact LEDs. In the life test, the power degradation of the p-In/sub 0.1/Ga/sub 0.9/N-ITO contact samples also exhibits a lower value than that of the conventional ones.     

A 1-/spl mu/m Bipolar VLSI Technology

A 1-/spl mu/m VLSI process technology has been developed for the fabrication of bipolar circuits. The process employs electron-beam slicing writing, plasma processing, ion implantation, and low-temperature oxidation/annealing to fabricate bipolar device structures with a minimum feature size of 0.9 /spl mu/m. Both nonisolated I/sup 2/L and isolated Schottky transistor logic (STL) devices and circuits have been fabricated with this process technology. The primary demonstration vehicle is a seated LSI, I/sup 2/L, 4-bit processor chip (SBP0400) with a minimum feature size of 1 /spl mu/m. Scaled SPB0400's have been fabricated that operate at clock speeds 3X higher than their full-size counterparts at 50-mA chip current. Average propagation delay has been measured as a function of minimum feature size for both I/sup 2/L and STL device designs. Power-delay products of 14 fJ for I/sup 2/L and 30 fJ for STL have been measured.     

/sup 60/Co gamma irradiation effects on n-GaN Schottky diodes

The effect of /spl gamma/-ray exposure on the electrical characteristics of nickel/n-GaN Schottky barrier diodes has been investigated using current-voltage (I-V), capacitance-voltage (C-V), and deep-level transient spectroscopy (DLTS) measurements. The results indicate that /spl gamma/-irradiation induces an increase in the effective Schottky barrier height extracted from C-V measurements. Increasing radiation dose was found to degrade the reverse leakage current, whereas its effect on the forward I-V characteristics was negligible. Low temperature (/spl les/50) post-irradiation annealing after a cumulative irradiation dose of 21 Mrad(Si) was found to restore the reverse I-V characteristics to pre-irradiation levels without significantly affecting the radiation-induced changes in C-V and forward I-V characteristics. Three shallow radiation-induced defect centers with thermal activation energies of 88 104 and 144 meV were detected by DLTS with a combined production rate of 2.12 /spl times/ 10/sup -3/ cm/sup -1/. These centers are likely to be related to nitrogen-vacancies. The effect of high-energy radiation exposure on device characteristics is discussed taking into account possible contact inhomogeneities arising from dislocations and interfacial defects. The DLTS results indicate that GaN has an intrinsically low susceptibility to radiation-induced material degradation, yet the effects observed in the Schottky diode I-V and C-V characteristics indicate that the total-dose radiation hardness of GaN devices may be limited by susceptibility of the metal-GaN interface to radiation-induced damage.     

4H-SiC UV photo detectors with large area and very high specific detectivity

Pt/4H-SiC Schottky photodiodes have been fabricated with the device areas up to 1 cm/sup 2/. The I-V characteristics and photoresponse spectra have been measured and analyzed. For a 5 mm/spl times/5 mm area device leakage current lower than 10/sup -15/ A at zero bias and 1.2/spl times/10/sup -14/ A at -1 V have been established. The quantum efficiency is over 30% from 240 to 320 nm. The specific detectivity, D/sup */, has been calculated from the directly measured leakage current and quantum efficiency are shown to be higher than 10/sup 15/ cmHz/sup 1/2//W from 210 to 350 nm with a peak D/sup */ of 3.6/spl times/10/sup 15/ cmHz/sup 1/2//W at 300 nm.     

Characteristics of Au/n-InP Schottky junctions formed on H2- and PH3-plasma treated surfaces

Characteristics of An/n-InP Schottky junctions formed onn-InP treated with hydrogen (H₂)-and phosphine (PH₃)-plasmas have been investigated. An enhancement of the barrier height up to 0.7 eV or more is observed for Schottky junctions processed sequentially with plasma treatment, laboratory air oxidation and Au evaporation. From the measurement of Schottky junctions formed by in-situ metallization immediately after H₂-plasma treatment, it is found that laboratory air oxidation permits an increase in the barrier height by about 0.1 eV. The annealing experiment of Schottky junctions treated with plasma reveals that the substantial part of the barrier height enhancement is caused by release of the Fermi level pinning due to hydrogen passivation of surface defects. Although both H₂- and PH₃-plasmas are effective in enhancing the barrier height, PH₃-plasma is preferable in respect to minimizing plasma-induced damage. In the case of H₂-plasma treatment deep electron traps with activation energies of 0.21 and 0.51 eV below the conduction band are generated at and/or near the surface of InP, while these traps are not detected after PH₃-plasma treatment.     

4H-SiC混合PN/Schottky二极管的研制

报道了4H-SiC混合PN/Schottky二极管的设计、制备和特性．该器件用镍作为肖特基接触金属,使用了结终端扩展（JTE）技术．在肖特基接触下的n型漂移区采用多能量注入的方法形成P区而组成面对面的PN结,这些PN结将肖特基接触屏蔽在高场之外,离子注入的退化是在1500℃下进行了30min．器件可耐压600V,在600V时的最小反向漏电流为1×10-3A/cm2．1000μm的大器件在正向电压为3V时电流密度为200A/cm2,而300μm的小尺寸器件在正向电压为3.5V电流密度可达1000A/cm2．     

High-performance, metamorphic In/sub x/Ga/sub 1-x/As tunnel diodes grown by molecular beam epitaxy

Thin In/sub x/Ga/sub 1-x/As tunnel junction diodes having compositions from x=0.53 to 0.75 that span a range of bandgap energies from 0.74 to 0.55 eV, were grown on InP and metamorphic, step-graded In/sub x/Al/sub 1-x/As/InP substrates using molecular beam epitaxy and evaluated in the context of thermophotovoltaic (TPV) applications. Both carbon and beryllium were investigated as acceptor dopants. Metamorphic tunnel diodes with a bandgap of 0.60 eV (x=0.69) using carbon acceptor doping displayed highest peak current densities, in excess of 5900 A/cm/sup 2/ at a peak voltage of 0.31 V, within a 200 /spl Aring/ total thickness tunnel junction. Identically doped lattice-matched tunnel diodes with a bandgap of 0.74 eV exhibited lower peak current densities of approximately 2200 A/cm/sup 2/ at a higher peak voltage of 0.36 V, consistent with the theoretical bandgap dependence expected for ideal tunnel diodes. Specific resistivities of the 0.60 eV bandgap devices were in the mid-10/sup -5/ /spl Omega/-cm/sup 2/ range. Together with their 200 /spl Aring/ total thickness, the electrical results make these tunnel junctions promising for TPV applications where low-resistance, thin metamorphic tunnel junctions are desired.     

Sub-500/spl deg/C solid-phase epitaxy of ultra-abrupt p/sup +/-silicon elevated contacts and diodes

A well-controlled low-temperature process, demonstrated from 350/spl deg/C to 500/spl deg/C, has been developed for epitaxially growing elevated contacts and near-ideal diode junctions of Al-doped Si in contact windows to the Si substrate. A physical-vapor-deposited (PVD) amorphous silicon layer is converted to monocrystalline silicon selectively in the contact windows by using a PVD aluminum layer as a transport medium. This is a solid-phase-epitaxy (SPE) process by which the grown Si is Al-doped to at least 10/sup 18/ cm/sup -3/. Contact resistivity below 10/sup -7/ /spl Omega//spl middot/cm/sup 2/ is achieved to both p/sup -/ and p/sup +/ bulk-silicon regions. The elevated contacts have also been employed to fabricate p/sup +/-n diodes and p/sup +/-n-p bipolar transistors, the electrical characterization of which indicates a practically defect-free epitaxy at the interface.