A computer-aided simulation model for the I–V characteristic of M-n-p silicon Schottky-barrier diodes produced by use of low-energy arsenic-ion implantation

Current-transport properties of Al-n-p silicon Schottky-barrier diodes have been studied both experimentally and theoretically. An analytical model for the I-V characteristic of a metal-n-p Schottky barrier diode has been developed by using an interfacial layer-thermionic-diffusion model. Assuming a Gaussian distribution for the implanted profile, the barrier-height enhancement and ideality factor have been derived analytically. Using low energy (25 KeV) arsenic implantation with the dose ranged form 8 × 10¹⁰/cm² to 10¹²/cm², Al-n-p silicon Schottky barrier diodes have been fabricated and characterized. Comparisons between the experimental measurements and the results of computer simulations have been performed and satisfactory agreements between these comparisons have been obtained. The reverse I–V characteristics of the fabricated Al-n-p silicon Schottky barrier diodes can also be well simulated by the developed model.     

Minority-carrier lifetime in dielectrically isolated single-crystal silicon films defined by electrochemical etching

The minority-carrier lifetime has been measured in thin, dielectrically isolated single-crystal silicon films defined by electrochemical etching. Both transient-current measurements on deep-depletion MOS transistors and recombination-current measurements on bipolar junction transistors have been use to determine the lifetime. Values of the order of 1 μ sec have been observed in both n-and p-type films with dopant concentrations of about 10¹⁵ cm^?3. It was found that the characteristics of the MOS transistors were not dominated by generation at either surface of the thin film. No differences were seen between the characteristics of bipolar transistors fabricated in the thin films and those of transistors fabricated in bulk control wafers.     

Electrical characteristics of r.f.-sputtered CdTe thin-films for photovoltaic applications

A method of preparing self-doped p- and n-type and In-doped n-type CdTe thin-films for photovoltaic applications has been developed using r.f. sputtering. Ohmic contacts to n-type films with contact resistivity less than 10^?2 Ω — cm² have been obtained. Schottky barrier diode test devices, formed by evaporation of various metals including Au on n-CdTe films, have been examined for electrical and photovoltaic evaluation of the sputtered films. Although S.B. diodes based on In doped films, prepared under Cd overpressure, show promising electrical and photovoltaic performance (V_oc ～ 315 mV, I_sc ～ 4.6mA/cm²), much improvement remains to be made by further control of dopant concentration and structural details of films.     

Ohmic contacts on n- and p-layers of GaAs using laser-induced diffusion

Thin surface layers of GaAs have been heavily doped by laser-assisted diffusion from the gas phase using H₂Se and Diethylzinc (DEZ) in H₂. The dependence of sheet carrier concentration and contact resistance of evaporated metal contacts on laser pulse energy, duration and substrate temperature is given. Specific contact resistances of 3·10^?5 ω cm² and 5·10^?5 ω cm² for nonalloyed n- and p-contacts, respectively, are obtained. After alloying they improve to values of 3·10^?6 ω cm². This process can be used to produce local ohmic contacts at low temperature.     

Simultaneous Formation of Ohmic Contacts on p +- and n +-4H-SiC Using a Ti/Ni Bilayer

In this work, Ti/Ni bilayer contacts were fabricated on both p ⁺- and n ⁺-4H-SiC formed by ion implantation, and the effects of the Ti interlayer on the contact resistance and interfacial microstructure were studied. Adoption of a thin (10 nm) Ti interlayer resulted in specific contact resistance of 4.8 μΩ cm² and 1.3 mΩ cm² on n ⁺- and p ⁺-4H-SiC, respectively, comparable to the values for contacts using only Ni. Moreover, contacts using Ti/Ni provide a flat and uniform interface between Ni₂Si and SiC, whereas discontinuous, agglomerated Ni₂Si islands are formed without the use of a Ti interlayer. In addition, the Ti interlayer was demonstrated to effectively dissociate the thin oxide film on SiC, which is advantageous for low-resistance, reliable ohmic contact formation. In summary, use of a Ti/Ni bilayer is a promising solution for one-step formation of ohmic contacts on both p ⁺- and n ⁺-4H-SiC, being especially suitable for SiC n-channel metal-oxide-semiconductor field-effect transistor (nMOSFET) fabrication.     

Interface studies of the MOS-structure by transfer-admittance measurements

The transfer-admittance of n- and p-channel MOS transistors has been measured under the condition of a uniform channel. These MOS transistors all showed a measurable “slow interface state drift” <0·1–0·2 V. The transfer-susceptance has been found to show a significant peak value in moderate inversion. Over the entire moderate and strong inversion region the transfer-susceptance remains constant as a function of the measurement frequency ω between 1·6 Hz and 2 × 10⁴ Hz, while the transfer-conductance varies almost like ln ω. Furthermore the transfer-susceptance shows a linear relationship with the variation of the transfer-conductance per frequency decade. The paper shows that these phenomena can be well explained by assuming a tunneling of channel charge carriers into electron states in the oxide. Also the temperature behaviour of the transfer-admittance does not seem to be in conflict with this tunnel model. More than the CV measuring method the measurement of the transfer-admittance allows an investigation of the interaction between mobile inversion layer charge carriers, and interface states in the condition of moderate inversion (5 × 10¹⁰-5 × 10¹¹ electrons cm^?2). The measuring method might therefore find application in the investigation of charge trapping in CCD devices. As a pertinent result the density of oxide states having time constants between 6 × 10^?1 sec and 1·6 × 10^?5 sec appears to increase to values of about 10¹¹ per cm²V as the interface state energy approaches the conduction and valence band edge energies within a distance of ? 70 meV.     

Electroless deposition as a means of obtaining ohmic contacts: Au/Pd onto GaAs

Autocatalytic gold deposits onto palladium-activated GaAs substrates, prepared by chemical displacement, have been found to produce good quality ohmic contacts (in the 10⁻⁵ Ω cm² range) provided that the Pd layer thickness and the annealing temperature are optimized. Pd plays the role of catalyst for the subsequent autocatalytic gold deposition; but by using thicker Pd films than necessary to fulfil this “chemical” part, this element also plays another prominent role in the metallurgy of the contact. A transmission electron microscopy (TEM) study has been carried out in order to characterize the growth of Pd nuclei on GaAs. The electrical measurements obtained on such alloyed Au/Pd/n or p-type GaAs contacts are analyzed in term of a graded amorphous/crystalline junction.     

Subnanosecond 4<Emphasis Type="Italic">H</Emphasis>-SiC diode current breakers

Mesa epitaxial 4H-SiC-based p ⁺-p-n ₀-n ⁺ diodes have been fabricated and their reverse recovery characteristics have been measured in modes typical of fast semiconductor current breakers, drift step recovery diodes, and SOS diodes. It has been found that, after the short (～10 ns) pulsed injection of nonequilibrium carriers by a forward current with a density of 200–400 A cm^?2 and the subsequent application of a reverse voltage pulse (with a rise time of 2 ns), diodes can break a reverse current with a density of 5–40 kA cm^?2 in a time of about (or less than) 0.3 ns. A possible mechanism for ultrafast current breaking is discussed.     

Characteristics of metal-semiconductor contacts fabricated by the electroless deposition method

Metal-semiconductor contacts have been fabricated by electroless deposition of Cu on chemically cleaned n-type silicon and their characteristics studied. The values of barrier height and the ideality factor are found to be comparable to those of vacuum evaporated contacts. A non-linearity in the 1/C² vs V plot has been observed and the same has been satisfactorily explained by taking surface state capacitance into consideration.     

Fabrication and some applications of large-area silicon field emission arrays

A method of fabricating large-area arrays of sharply-pointed field emitters at densities up to 1·5 × 10⁵ per cm² from single crystal silicon wafers is described. The point emitters are formed by etch-undercutting a precision oxide pattern which is delineated on the silicon surface by projection photolithography. Observations indicate that emitters with very small tip dimensions in the 200Årange are formed. In the presence of an external electric field, such as produced by a voltage applied to a closely-spaced, planar anode, multiple-emitter arrays are shown to field-emit electrons uniformly over areas up to 3 cm dia. Two important applications currently being explored, are discussed: (1) High resistivity, p-Si has been utilized to develop experimental field emission photocathodes with which field emission imaging has been demonstrated. These photoemitters exhibit very high photo-sensitivities at visible and near i.r. wavelengths. For example, at 0·86 μm, the measured quantum efficiency is 25 per cent which is about five-times higher than the red-sensitive S-20 photocathode and comparable to the highest reported sensitivities of the III–V photosurfaces; (2) N-type emitter arrays show considerable promise as high current, cold cathodes and total emission currents of 1/4 A from 1 cm² areas of 100 Ω-cm n-type emitters have been obtained. Measurements were made under pulse conditions because of anode dissipation considerations.     

Aluminum-silicon ohmic contact on “shallow” n+p junctions

In this work various technologies for contacts of Al on n⁺Si have been experimentally investigated, particularly in view of their suitability to very shallow $\text{n}\text{p}$ junctions.Special test-patterns have been used to measure the contact resistivity, while diodes reverse current density has been checked to evaluate the junction leakage induced by the aluminum-silicon interaction during sintering.Best results are obtained by depositing a thin polysilicon layer on the front surface before the doping process and the Al evaporation. In this case both the requirements of low contact resistivity (< 10^?4 ohm · cm²) and low junction leakage current are satisfied. Comparison with the conventional Al/Si and AgTi/Si ohmic contacts has been performed.     

Electrical and photoelectric properties of anisotype n-TiN/p-Si heterojunctions

Photosensitive n-TiN/p-Si heterojunctions are fabricated by the reactive magnetron sputtering of a thin titanium-nitride film with n-type conductivity onto polished polycrystalline p-Si wafers. The I–V characteristics of the heterostructures are measured at different temperatures. The temperature dependences of the potential-barrier height and series resistance of the n-TiN/p-Si heterojunction are studied. The dominant mechanisms of current transport through the heterojunction in the cases of forward and reverse bias are established. The heterostructures generate the open-circuit voltage V _oc = 0.4 V and the short-circuit current I _sc = 1.36 mA/cm² under illumination with a power density of 80 mW/cm².     

The specific contact resistance of Pd2Si contacts on n- and p-Si

The specific contact resistance ρ_c of Al and Pd₂Si contacts has been measured on p- and n-Si substrates of uniform resistivity. The variation of ρ_c with substrate resistivity is described by the following equations:

The specific contact resistance of Al contacts was found to be lower than the values of Pd₂Si contacts on p-Si. Pd₂Si contacts on both n- and p-Si, (111) orientation, become non-ohmic in the resistivity range $\text{0.020?0.10 Ω-}\text{cm}$.The data in this study are not sufficient to distinguish a variation in ρ_c with substrate orientation. Specific contact resistance values of Pd₂Si contacts on $\text{0.005 Ω-}\text{cm}\text{(100) n-}\text{Si}$ and $\text{0.010 Ω-}\text{cm}\text{(100) p-}\text{Si}$ were not significantly different from values expected for the (111) substrates.     

“Ideal” static breakdown in high-voltage (1 kV) 4<Emphasis Type="Italic">H</Emphasis>-SiC<Emphasis Type="Italic">p-n</Emphasis> junction diodes with guard ring termination

Nearly “ideal” static high-voltage breakdown (1060 V) in 4H-SiC p⁺-n-n⁺ diodes with guard ring termination is observed. At the doping level of 1.9 × 10¹⁶ cm^?3 in the n-type base, the diode breakdown field is 2.7 × 10⁶ V/cm. At the reverse bias as high as 1000 V, the leakage-current density does not exceed 5 × 10^?5 A/cm². The diodes withstand without degradation an avalanche-current density of 1 A/cm², which corresponds to the dissipated power of 1 kW/cm².     

Doping and temperature dependences of minority-carrier diffusion length and lifetime deduced from the spectral response measurements of p-N junction solar cells

The minority-carrier diffusion length in the base region of p⁺?n (n⁺?p) junction solar cells has been deduced from the relative spectral response in the long wavelength. The doping and temperature dependences of minority-carrier diffusion length have also been characterized. It has been shown that the minority-carrier diffusion length is slightly increased with increasing temperature and is decreased with increasing doping concentration. Based on the known minority-carrier diffusivity as functions of doping concentration and temperature, the doping and temperature dependences of minority-carrier lifetimes have been deduced. It has been verified that the empirical relationship between minority-carrier lifetime and doping concentration deduced by other method is in good agreements with our experimental measurements. Moreover, it has been shown that the minority-carrier lifetime is increased with increasing temperature, which is consistent with that measured by the open-circuit voltage decay (OCVD) method.     

Minority carrier lifetimes in silicon solar cells determined from spectral and transient measurements

Measurements of the spectral collection efficiency and short circuit current decay rate following an X-ray pulse have been made on three types of single crystal silicon solar cells. The cell types were n⁺ - p, p⁺ - n, and p⁺ - n - n⁺ with base resistivities of 0.3, 10 and 10 Ω-cm, respectively. Minority carrier lifetimes were determined from both experiments using analytical or device code calculations, as required. For the n⁺ - p and p⁺ - n cells, nominal lifetimes of 2 and 5 ωsec, respectively, were obtained. A lifetime greater than 100 ωsec was inferred for the p⁺ - n - n⁺ device. This value represents a minimum estimate since our analysis is inaccurate when the diffusion length exceeds the cell thickness, as is the case here. The difference in base lifetime for the p⁺ - n and p⁺ - n - n⁺ structures is attributed to gettering during the phosphorus diffusion to form the back surface field layer.     

Low resistance ohmic contacts to n- and p-InP

The contact properties of various metal combinations, deposited by vacuum evaporation on InP, were studied. Among these metal combinations, Au/Ge + Ni and Au/Zn proved to be most suitable. The former on n-InP (n = 8 × 10¹⁷/cm³) and the latter on p-InP (p = 9 × 10¹⁷/cm³) exhibited specific contact resistances as low as 1.2 × 10^?6 and 1.1 × 10^?4 Ωcm², respectively. The specific contact resistances were analyzed using a four-point method which also accounts for the spreading resistance. Furthermore, the resistances of metal contacts to InP were calculated as a function of doping concentration and were compared with the experimental results. The described contacting technique was successfully applied to the preparation of quaternary lasers.     

Electrical properties of proton-irradiated CdSnAs2

Electrical properties and isochronal annealing of proton-irradiated (5 MeV, 2 × 10¹⁶ cm^–2) n-and p-type CdSnAs₂ crystals have been studied. The limiting electrical parameters of the irradiated material were determined: Hall constant 〈R _H〉 ≈ ?1.2 cm³/C, electrical conductivity 〈σ〉 ≈ 1350 Ω^?1 cm^?1, Hall mobility 〈|R _H|〉〈σ〉 ≈ 1500 cm²/(V s), and Fermi level position F _lim ≈ 0.43–0.45 eV above the valence-band top. The energy position of the “neutral” point for the CdSnAs₂ compound was calculated.     

Effect of low-temperature annealing on characteristics of SiC detectors with radiation-induced defects

p ⁺-n-n ⁺ detector structures based on CVD films with an uncompensated donor concentration of 2 × 10¹⁴ cm^?3 have been studied. The p ⁺-region was created by implantation of Al ions. The detectors were preliminarily irradiated with 8-MeV protons at a fluence of 3 × 10¹⁴ cm^?2 and then annealed at 600°C for 1 h. In measurements performed in the temperature range 20–150°C, the forward-and reverse-bias modes were compared. It is shown that the annealing leads to a higher collection efficiency of carriers generated by nuclear radiation and to a decrease in the amount of charge accumulated by traps in the course of testing. Despite the positive effect of the annealing, a considerable amount of radiation defects remain, which is manifested, in particular, in the kinetics of the forward current.     

High-efficiency (49%) and high-power photovoltaic cells based on gallium antimonide

High-efficiency GaSb-based photovoltaic cells designed for conversion of high-power laser radiation and infrared radiation of emitters heated by concentrated solar radiation are fabricated and studied. The maximum efficiency of conversion of the radiation with λ = 1680 nm was 49% at the photocurrent density of 50–100 A/cm² for the fabricated photovoltaic cells. The methods for reducing the losses at ohmic contacts to p-and n-GaSb are investigated. The minimum values of the specific resistance, (1–3) × 10^?6 Θ cm², of contact to p-GaSb with the doping level of 10²⁰ cm^?3 were obtained using the Ti/Pt/Au contact system. The minimum values of the specific contact resistance were (1–3) × 10^?6 Θ cm² in the case of n-GaSb with the doping level of 2 × 10¹⁸ cm^?3 if the Au(Ge)/Ni/Au and Au/Ni/Au contact systems are used.