Schottky barriers on InSb

Schottky barriers formed on air-cleaved InSb are found to be more reproducible and have less leakage than diodes fabricated by chemical processing. Etched surfaces yield diodes with large leakage currents and high series resistances whose values are correlated, i. e. , high series re-sistances have less leakage and vice versa. With air-cleaved surfaces the lowest leakage is observed when the surfaces adjoining the contact are covered with SiO₂. From C^-2 versus V data, barrier heights of 50 mV and 175 mV at 77K are measured for Au contacts to n- and p-type InSb, respectively. The current-voltage characteristics of Au contacts are consistent with these barriers, but the low-temperature field-emission behavior appears to be dom-inated by tunneling via traps. For Pb contacts, deep-level traps are in evidence that can lead to erroneous in-terpretations of C^-2 versus V voltage intercepts. The I-V data for Pb contacts suggest V_Bn ≈0 and V_Bp ≈E_g/q. Diodes fabricated on vacuum-cleaved surfaces have large leakage currents which result from the etching procedures introduced to isolate individual diodes.     

Low-frequency noise properties of GaN Schottky barriers deposited on intermediate temperature buffer layers

Metal–semiconductor–metal (MSM) structures were fabricated by RF-plasma-assisted MBE using different buffer layer structures. One type of buffer structure consists of an A1N high-temperature buffer layer (HTBL) and a GaN intermediate temperature buffer layer (ITBL), another buffer structure consists of just a single A1N HTBL. Systematic measurements in the flicker noise and deep level transient Fourier spectroscopy (DLTFS) measurements were used to characterize the defect properties in the films. Both the noise and DLTFS measurements indicate improved properties for devices fabricated with the use of ITBL and is attributed to the relaxation of residue strain in the epitaxial layer during growth process.     

Schottky barriers on single-crystal indium telluride

Schottky barriers on single-crystal p-In₂Te₃ were formed with evaporated films of materials Al, Ag and Cu with work-functions Ø_M<(E_g+x_s) while Au, Ni and Pd films with larger Ø_M produced ohmic contacts. The barrier heights were found to be 0.72, 0.67 and 0.69 eV respectively, while the ideality factors were 1.15, 3.48 and 6.54. The interface index s was 0.16 compared with the theoretical value of 0.146, its small magnitude indicating the covalent nature of the semiconductor. Barriers on n-In₂Te₃ showed Ø_bn + Ø_bp = 1.29 eV compared with E_g = 1.12 eV. A surface-state rather than a chemical bonding theory provided a satisfactory explanation of the results.     

Aluminium Schottky barriers on sputter-etched silicon

Schottky barriers have been prepared by sputter-etching a silicon surface immediately prior to the deposition, by sputtering, of an aluminium electrode. The barrier height measured on these diodes is nearly identical to the height found previously for barriers made by cleaving silicon in a vacuum in a stream of evaporating aluminium species. This suggests that the barrier height is controlled by surface states.     

Schottky barriers on n-GaN grown on SiC

Characteristics of Schottky barriers fabricated on n-type GaN were investigated. The barriers were formed by vacuum thermal evaporation of Cr, Au, and Ni. Current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the barriers were measured in a wide temperature and current density range. Fundamental parameters (barrier height and built-in potential) of the Schottky barriers were determined. The dependence of the barrier ideality factor on doping concentration in GaN was measured. Correlation between the barrier height and metal work function was observed. The electron affinity for GaN was determined using both C-V and I-V characteristics. The current flow mechanism through the barriers is discussed.     

表面处理对肖特基接触的影响

研究了不同的表面处理方法对器件肖特基特性的影响。实验结果表明,采用氧等离子体及体积比(HF:NH_4F)为1:7的BOE溶液对Al Ga N/Ga N异质结材料表面进行处理后,其肖特基接触特性比盐酸或者氨水溶液处理有了明显的改善。当栅压为–50 V时,栅反向漏电仅为3.8×10~(–5) A/mm,相比降低了1~2个数量级。另外,电容电压CV测试结果显示,经过BOE溶液处理表面,明显降低了器件表面态密度,达到1013cm~(–2)·e V~(–1)量级,表面态密度的降低,提高了肖特基势垒高度,降低了隧穿电流和表面漏电。     

Schottky barriers on atomically clean cleaved GaAs

We report here the first systematic study of the electronic properties of Al, Au, Ag and Cu Schottky barrier diodes on n-type GaAs. These diodes were formed on cleaved (110) surfaces in ultra-high vacuum (UHV) using similar conditions and evaporation rates during the initial stages of Schottky barrier formation as in the photoemission spectroscopy (PES) studies. Barrier height determinations using device measuring techniques (current-voltage (I–V), capacitive-voltage (C–-V) and internal photoemission) are compared with the results from the PES studies. Essentially identical barrier heights are found from PES and the electrical measurements for the noble metals. The barrier height of the noble metal: n-GaAs system (0.9 eV) is larger than any simple metal on n-type GaAs previously reported. This is examined in light of recent work by Zur, McGill and Smith [22] and a model is suggested to explain it. Results of this study are found to be consistent with the unified defect model which has hypothesized that the barrier height is established by the energy levels of structural defects formed at the surface during the metal deposition.     

Schottky rectifiers on silicon using high barriers

Schottky diodes are presently used for power rectification because of their low forward voltage drop. However, they have only been fabricated on relatively low resistivity and thin semiconductor layers. Hence the reverse breakdown voltages are low. To make diodes that stand higher reverse voltages, low doped material of sufficient thickness is necessary. Ordinary Schottky barriers do not inject minority carriers and the resistive voltage drop at high forward currents will be large, However, for high Schottky barriers ～ 0.9eV, minority carriers are injected and the series resistance is decreased.In this paper we report results from one-dimensional numerical calculations as well as experimental results of high barrier Schottky diodes. We discuss the voltage drop at high forward currents for different substrate resistivity and thickness, as well as values of the high barrier.     

PV on noise barriers

PV on noise barriers has been around for 14 years. During this time considerable progress has been achieved not only on the PV module technology, but also in the construction of photovoltaic noise barriers (PVNB). The first plant was built in Switzerland in 1989; at present there are numerous plants with a total documented power of about 850 kW_p in operation in Europe. This paper gives a short overview on the progress and state of the art of PVNB in Europe. Copyright © 2004 John Wiley & Sons, Ltd.     

Laser formation of Pt-Si Schottky barriers on silicon

135 nsec pulses ofλ = 1.06μm light from a Nd: YAG laser have been used to form Schottky barriers by irradiation of a 500Å thick metal film on n-type silicon. Large area barriers were fabricated by over-lapping individual 30μ diameter laser pulses of from 4 to 12 J/cm². The barrier height was 0.73 ± 0.03 V, independent of the laser power. The barrier quality, as assessed by measurement of the forward current characteristic, decreased with laser power to a value of n = 1.5 at 12 J/cm².     

On the width of Schottky barriers

The paper presents numerical computations of the Schottky barrier width, made by taking the free carrier space charge into account, and points to substantial discrepancies between the actual and conventionally assumed volume as a function of current.     

Excess capacitance and non-ideal Schottky barriers on GaAs

Non-ideal $\text{1}\text{C}{}^2$ vs V plots showing curvature concave downwards can be transformed into linear $\text{1}\text{(C ? C}{}_0\text{)}{}^2$ vs V plots by determining the excess capacitance, C₀, as the intercept of a C vs $\text{(V + V}{}_{\mathrm{d}}\text{)}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ plot, where V_d is the diffusion potential. The corrected curves indicate a uniform doping profile in agreement with independent Van der Pauw measurements. An analysis of the possible significance of C₀ indicates that its value can be used as an approximate quality index for materials fabricated by different methods.     

Low-frequency noise in Schottky barrier diodes

The low-frequency excess noise in Schottky barrier diodes has been investigated. In the ideal case where the saturation current is completely determined by thermionic emission of electrons, no 1/? noise will be produced in the barrier. The presence of trap states in the depletion region can lead to generation-recombination noise. At sufficient high forward currents 1/? noise can be generated in the series resistance of the Schottky diode. Deviations from the ideal diode, for example as a result of edge effects, produce 1/? noise and increase at the same time the ideality factor. It is empirically found that the 1/? noise level decreases very rapidly if the ideality factor tends to unity.     

Hopping conductivity and dielectric relaxation in Schottky barriers on GaN

A study of the current and capacitance dependences on the forward voltage in Au/n-GaN Schottky diodes, the sub-band optical absorption spectra, and the defect photoluminescence in n-GaN bulk crystals and thin layers is reported. It is shown that defect-assisted tunneling is the dominant transport mechanism for forward-biased Schottky contacts on n-GaN. The dependences of the current and capacitance on forward bias reflect the energy spectrum of defects in the band gap of n-GaN: the rise in the density of deep states responsible for yellow photoluminescence in GaN with increasing energy and the steep exponential tail of states with an Urbach energy of E _U = 50 meV near the conduction-band edge. A decrease in the frequency of electron hops near the Au/n-GaN interface results in a wide distribution of local dielectric relaxation times and in a dramatic transformation of the electric-field distribution in the space-charge region under forward biases.     

Infrared optoelectronic properties of metal-germanium Schottky barriers

An experimental study has been made of the electronic properties of rectifying metal-Ge (n-type) contacts for a range of metals (Au, Cu, Ag, Pb, and Ni) and their optoelectronic characteristics under monochromatic illumination for λ = 0.6328 µm and for 1 µm < λ ≲ 2 µm in the near infrared. For each metal, very idealI-Vcharacteristics were obtained withnvalues from the exponential forward bias region of 1.02 to 1.08 and excellent reverse saturation at 300 K. The dependence of photoresponse on thickness of various metal electrodes (from 50 to more than 1000 Å) was observed.phi_{B}'sfound fromIV C-V, and photoresponse measurements are in close agreement within ±0.03 eV. The dependence of quantum efficiency (QE) upon metal thickness was measured for all metals and these results exhibit the expected decline in QE withd gsim 100Å. Ford lsim 100Å, QE can be as high as 75 percent at λ = 6328 Å, and 48 percent in the wavelength range 1.1 µm < λ < 1.4 µm. QE versushv(1 µm < λ < 2 µm) measurements have identified thresholds for the indirect and direct band-to-band excitation in the germanium and for the internal photoemission of electrons from the metal over the Schottky barrier induced by absorption of the infrared photons.     

Trap distribution in gold-refractory/GaAs Schottky barriers

Interfacial and bulk traps are shown to be introduced in GaAs Schottky barriers as a result of metal deposition. Majority carrier and minority carrier traps are correlated with degradation in field effect transistor properties. The interface traps are present in both the sputtered and electron beam evaporated layers.     

Power law reverse current-voltage characteristic in Schottky barriers

A power law relationship between the reverse current and reverse voltage is computed theoretically using a model involving an exponential distribution of interface states. The model correlates Schottky barrier data on large bandgap semiconductors such as ZnO and GaP where the reverse current is proportional to the sixth power of the reverse voltage.     

Behavior of various silicon Schottky barrier diodes under heat treatment

Variations of Schottky forward voltage with heat treatment have been observed for AlPd₂Si Si and Si-doped AlPd₂Si Si Schottky barrier diodes. These variations have been reduced to a minimum by the use of a barrier metal such as TiW between Al and the silicided contacts.     

Control of the height of Schottky barriers on MBE GaAs

The effective Schottky barrier height of nickel on gallium arsenide has been varied between 0.48 eV and 0.96 eV by using MBE to grow a range of thin heavily doped layers. Barrier lowering has been achieved with n-type layers doped with silicon or tin and barrier raising with p-type layers doped with beryllium. The ideality factor of the diodes was less than 1.2 in all cases.