Noise in epitaxial silicon bulk unipolar diodes

Silicon camel diodes with barrier heights in the range 0.46?0.94 eV were realised by means of low-pressure vapour phase epitaxy (LPVPE). These diodes show a conversion loss as low as 4.2 dB at 2 GHz and a noise figure of 4.8 dB.     

Bulk unipolar camel diodes formed using indium implantation into silicon

Bulk unipolar camel diodes have been made by implanting indium and arsenic into 〈100〉 silicon at low energies. It is found that a wide range of barrier heights can be obtained simply by selecting the indium energy, ideality factors being <1.1 in some cases, and leakage currents <150 nA cm^-2following activation of the implants at 650°C.     

Amorphous silicon/silicon carbide heterojunction bulk unipolar diodes (HEBUD)

A new hydrogenated amorphous silicon/silicon carbide heterojunction bulk unipolar diode (HEBUD) has been successfully fabricated. The sawtooth-shaped composition wave of α-SiC:H between layers of n-type α-Si:H was made on an ITO/glass substrate by the RF glow-discharge deposition method. Rectification produced by an asymmetric potential barrier is demonstrated. Preliminary results showed that the design principle is feasible, and that the device is stable. The capacitance was constant regardless of bias. A switching time of 15 µs and a propagation delay time of 9 µs were obtained.     

LPVPE-grown silicon camel diodes

Low-pressure vapour-phase epitaxy (LPVPE) was applied to fabricate multilayer structures like camel diodes. Using in situ doping and selective growth, camel diodes with good ideality factors (1.08?1.2) and low generation-recombination currents were realised.     

Millimeter-wave bulk unipolar mixer diodes

The use of a bulk unipolar camel diode as a mixing element is considered. A diode of this type is shown to have a conversion loss of between 7 and 8 dB over the frequency range 27 to 35 GHz, with a similar SSB noise figure.     

Theory of triangular-barrier bulk unipolar diodes including minority-carrier effects

The effect of the minority-carrier charge on the barrier height of the triangular-barrier (TB) majority-carrier diode is considered. The consequences of this effect on the device performance as a diode, transistor, photodetector, and a thyristor is briefly delineated. A two-carrier model of the TB diode is developed to account for this effect. Four other approximate models of the TB diode are compared with the two-carrier model, and the range of their validity established. A high-gain TB "transistor" is proposed based on the mechanism of barrier-height modulation via minority-carrier injection in the TB diode.     

Formation of bulk unipolar diodes in hydrogenated amorphous siliconby ion implantation

Bulk unipolar diodes with a wide range of barrier heights have been made in hydrogenated amorphous silicon by ion implantation. The precise concentration of dopant atoms that can be obtained when implanting into an amorphous substrate leads to accurate barrier height control. Compared with the alternative unipolar device, the Schottky diode, these devices should provide uniform, high barrier diodes for photodetectors, and very low barrier diodes for low-power, unbiased, mixers and detectors     

Surface effects on breakdown characteristics of GaAs bulk diodes

Effects of peripheral-surface damages on breakdown characteristics ofn^{++}-n-n^{+}epitaxial GaAs bulk diodes were investigated experimentally. Critical voltages for switching from a high-voltage saturating-current state to a high-current low-voltage state were measured on a number of mechanically diced cubic-type elements and on chemically etched mesa-type elements. It was found that the switching voltages of the mesa-type diodes were much higher and more uniform than those of the cubic type. The difference in the switching voltages between the two types is ascribed to the peripheral-surface damages produced on the cubic-type elements during wire saw cutting. It was concluded that the elimination of the peripheral surface damages is important to obtain GaAs bulk diodes of high reliability.     

Microwave characteristics of BARITT diodes based on silicon carbide

Microwave characteristics of barrier-injected (BARITT) diodes made of silicon carbide are investigated. It is shown that the negative resistance of p⁺-n-p⁺ structure made of different polytypes of SiC is an order of magnitude higher in absolute value in comparison with the Si p⁺-n-⁺ structure, all other factors being equal, even in the absence of trap levels (TLs). It is shown also that the dynamic negative resistance, in absolute value, the power output and efficiency increase with an increase of the concentration of traps. The effects of TLs in the band gap of the semiconductor on the impedance, power output, and efficiency of SiC BARITT diodes are examined,     

Probability characteristics of electrical noise in heterojunction light-emitting diodes

A hardware-software complex for measurements of the characteristics of electrical and optical noise in light-emitting diodes (LEDs) in the frequency range from 1 to 40 kHz is described. The electrical noise of several types of heterojunction-based LEDs are studied; these types include red-emission LEDs with AlInGaP/GaAs quantum wells and the green- and blue-emission LEDs with AlInGaN/SiC quantum wells are studied by the method of discrete samples. The spectra of all studied LEDs in the frequency range from 1 to 10 kHz have the form 1/f ^γ. It is noteworthy that, for red-emission LEDs, the exponent γ is significantly smaller than unity; this index is close to unity for the green- and blue-emission LEDs. The characteristic time of correlation of the noise of red-emission LEDs by several times exceeds the correlation times for the blue- and green-emission LEDs. It is shown that reduced functions of the amplitude distribution of the noise voltage are close to Gaussian functions with almost the same dispersion for all LED types.     

Processing of unipolar diodes with electron beams

Low-energy ion implantation and multiple-scan electron-beam annealing have been used to produce bulk unipolar camel diodes and Schottky diodes with a range of barrier heights. Optimisation of results required precise doping and diffusion control.     

The electrical characteristics of 4H-SiC schottky diodes after inductively coupled plasma etching

The electrical characteristics of metal contacts fabricated on 4H-SiC have been investigated. Sputtered nickel ohmic contacts have been successfully produced on untreated 4H-SiC substrates and 4H-SiC surfaces cleaned with aggressive chemicals and ion sputtering. The current-voltage (I–V) characteristics of asdeposited contacts are observed to be nonohmic on all surfaces. After annealing at 1,000°C in a N₂ atmosphere, the contacts are seen to become ohmic with considerably less annealing time being required for the samples exposed to aggressive cleaning stages. Schottky diodes were then produced on the silicon carbide (SiC) surface after etching in an SF₆/O₂ inductively coupled plasma (ICP) for 3 min at varying substrate bias voltages and also on an untreated surface used as a control sample. The ideality factors of all diodes formed on the etched surfaces increased in comparison to the control sample. The highest ideality factor was observed for the diodes produced after etching at −0-V and −245-V bias voltage. A two-diode and resistor model was applied to the results that successfully accounted for the excess leakage paths. The defect density of each SiC surface was calculated using both the measured and the simulated ideality factors. An annealing stage was successful at reducing the ideality factors of all the diodes formed. The defect density calculated using the measured ideality factors of the annealed diodes was seen to have been reduced by an order of magnitude.     

Unified analysis of the bulk unipolar diode

A generalized model of the bulk unipolar diode (BUD) is analysed which allows for a direct comparison between the special cases of the Camel diode, the triangular barrier (TB) or planar doped barrier (PDB), and the p-plane barrier. The latter forms have been discussed separately in the literature but as yet no comparison has been made. Closed-form expressions for the functional dependence of the barrier heights on the applied voltage are obtained.     

Influence of radiation defects on electrical losses in silicon diodes irradiated with electrons

Silicon diodes with a p ⁺-n junction irradiated with 3.5-MeV electrons (the fluence ranged from 10¹⁵ to 4 × 10¹⁶ cm⁻²) have been studied. It is established that the dependence of the tangent of the angle of electrical losses tanδ on the frequency f of alternating current in the range f = 10²−10⁶ Hz is a nonmonotonic function with two extrema: a minimum and a maximum. Transformation of the dependences tanδ(f) as the electron fluence and annealing temperature are increased is caused by a variation in the resistance of n-Si (the base region of the diodes) as a result of accumulation (as the fluence is increased) or disappearance and reconfiguration (in the course of annealing) of radiation defects. The role of time lag of the defect recharging in the formation of tanδ(f) is insignificant.     

Argon-ion bombardment effects on the electrical characteristics of platinum-silicon Schottky diodes

Before barrier metal evaporation, silicon Schottky diodes were cleaned by argon-ion bombardment. Some device series were evaporated just after the ion cleaning, whereas others were annealed beforehand. The electrical characteristics of the different series were checked by means of standard I/V and C/V measurements. Whereas the ideality coefficient and the barrier height obtained from I/V characteristics showed nearly complete recovery after heat treatment for 1 h at 700°C, the barrier height from C/V measurements did not recover.     

Optical and electrical current gain in an amorphous silicon bulk barrier phototransistor

An amorphous silicon (a-Si) bulk barrier phototransistor was successfully fabricated on a glass substrate. The measured optical gain G and electrical current gain HFEare 196 percent and 11.8, respectively. Estimation and measurement methods for G and HFEare discussed.     

Structure and electrical characteristics of silicon field emissionmicroelectronic devices

Field emission current was measured from arrays of wet chemically etched silicon cold-cathode diodes. Two types of cathode tips were measured both as-etched and after sharpening by low-temperature oxidation. The field enhancement increase resulting from tip sharpening is less than expected from simulation. The currents measured follow a Fowler-Nordheim characteristic and are temperature insensitive from 130 to 360 K. Turn-on voltage is near 4 V, a value much less than measured from most other field emission sources. With a 920-nm anode-cathode spacing, a minimum 0.2-μA current per cathode was found. Telegraph noise of about 1% at 20 V was observed. These sharpened silicon tips are a viable cold cathode for vacuum microelectronics and other electron device applications     

Effects of the undoped layer on characteristics of amorphous silicon Schottky diodes

The effects of undoped layer thickness on the dark and illuminated I-V characteristics of hydrogenated amorphous silicon Schottky barrier solar cells are investigated. Schottky barrier (S.B.) metals having different work function (Cr and Pd) were deposited on the 0.22 µm - 1.45 µm thick a-Si:H films. Photovoltaic performance, Jsc, Voc, FF and efficiency, are independent of thickness of the undoped layer if film thickness is larger than the depletion region width. Jscand Vocare controlled by S.B. metal and FF is independent of S.B. metal. Dark I-V characteristics depend on both S.B. metal and device thickness suggesting a barrier controlled space charge limited phenomena. Variation of turn-on (threshold) voltage with undoped layer thickness can be applied to the design of switching and memory devices.     

Structure and electrical characteristics of epitaxial palladium silicide contacts on single crystal silicon and diffused P-N diodes

Pd₂Si contacts to single crystal silicon have been made by depositing Pd at room temperature and annealing at a succession of elevated temperatures. The silicide initially formed is a single crystal, even at room temperature. Its crystal structure is uniquely related to that of the underlying silicon with the basal plane of Pd₂Si making an excellent match, with respect to silicon atom positions, with the (111) plane of silicon. Understanding this epitaxy leads to an appreciation of the excellent electrical characteristics of these contacts which are shown to be superior to alloyed aluminum. For comparison, barrier height measurements reproduce earlier results of Kircher on Pd₂Si formed during a high temperature (200°C) deposition of Pd.