Decrease In Collector Current Research Articles

Damage Separation in a Bipolar Junction Transistor Following Irradiation With 250-MeV Protons

Irradiation of 2N5339 n-p-n bipolar junction transistors (BJTs) with either 250-MeV protons or 10-keV X-rays shifts the input characteristics to lower values of $V_{\mathrm {BE}}$ while degrading the current gain and drive current. The degradation is consistent with increased recombination in the neutral base and emitter–base (E–B) depletion region. A decrease in collector current following proton irradiation suggests that recombination in the neutral base is significant. At a given ionizing dose, degradation is worse for proton irradiation than for X-ray irradiation due to the presence of displacement damage and a higher charge yield. A comparison of degradation produced by the two radiation sources suggests that ~40% of the excess base current resulting from 250-MeV proton irradiation is due to ionization damage. When compared with previous results for other devices, these results suggest that ionization-to-displacement damage ratios in bipolar devices may increase with proton energy in a way that is consistent with trends in charge yield and non-ionizing energy loss (NIEL).

Van der Waals 2D layered-material bipolar transistor

Ultrathin and light heterojunction bipolar transistors based on two-dimensional (2D) layered materials with flexible semiconducting properties have been considered for several electronic applications. In this paper, a van der Waals p-BP/n-MoS2/p-BP BJT is demonstrated. It is fabricated using mechanical exfoliation, where a dry transfer technique is used to stack a vertical double heterojunction. The device structure includes nanoflakes of black phosphorus (BP) and MoS2. The current–voltage characteristics of the common–emitter and common–base configurations are examined. These p-BP/n-MoS2/p-BP bipolar transistors exhibit current–voltage characteristics similar to those of conventional p-n-p bipolar transistors. Devices with thin MoS2 layers show good saturation current–voltage characteristics, and a maximum common–emitter current gain (β = IC/IB) of approximately 10.1 is obtained at room temperature (300 K). Furthermore, the thickness dependence of the base region (n-MoS2) is investigated for the common–emitter output electrical characteristics (VCE − IC) of a double heterojunction bipolar transistor in which the emitter is grounded. The collector current decreases as the thickness of n-MoS2 is increased. This study can pave the way for the application of 2D materials as controllable amplifiers in flexible electronics.

A New Proportional Base Drive Technique for SiC Bipolar Junction Transistor

As one of the most attractive postsilicon power semiconductor devices, SiC bipolar junction transistor (BJT) has been studied extensively and commercialized in the past few years. However, SiC BJT has not been widely accepted in the market partially because of high driver consumption in the on-state, which is induced by a relatively large constant base current in order to ensure it is fully turned on . In this paper, a new proportional base driver with a simple circuitry is proposed in order to reduce the steady-state base driver consumption of SiC BJT. It utilizes a silicon small-signal mosfet as a variable resistor placed between the driver and the base of the SiC BJT. The collector current of the SiC BJT is measured via a Hall current sensor whose output is connected to the gate of the mosfet . When the collector current decreases, the gate voltage of the mosfet decreases and its on-state resistance increases, resulting in the decrease of the actual base driver current of the SiC BJT. The operation principle of the proposed proportional base drive technique has been verified by theoretical analysis and experimental demonstration of a 1200 V 10 A-SiC BJT-based dc–dc boost converter. Theoretical calculation, PSpice simulation, and experimental results have shown that the steady-state power consumption of the SiC BJT's proportional base driver is reduced by approximately 70% under the light load condition compared to conventional base driver with a constant base current.

Collision Cascade and Spike Effects of X-ray Irradiation on Optoelectronic Devices

Bombardment with high energy particles and photons can cause potential hazards to the electronic systems. These effects range from degradation of performance to functional failure, which can affect the operation of a system. Such failures become increasingly likely as electronic components are getting more sophisticated, while decreasing in size and tending to a larger integration. In this paper, the effects of X-ray irradiation on a plastic encapsulated infrared light emitting diode, coupled to a plastic encapsulated silicon infrared phototransistor, with both of them being electrically isolated at ON and OFF modes, are investigated. All the devices are exposed to a total dose of up to 1000 mAs. The electrical parameters of the optoelectronic devices during the radiation exposure and at post-irradiation are compared to the pre-irradiation readings. The findings show that the highest degradation occurs at low dose of exposure; beyond 100 mAs the relative decrease in collector current of the phototransistor is gradually reduced. The most remarkable feature found, is the operational dependence of the bias collector current, indicating a higher degradation for low bias forward current of the light emitting diode. The degradation induced at the forward current of the light emitting diode by X-rays irradiation is almost negligible whereas a decrease of the rate of change in current transfer ratio is significant during the X-ray irradiation. The results show that there is no significant difference between current transfer ratio of ON mode and OFF mode radiation. It is observed that the operating mode of the optoelectronic devices after exposure to 1000 mAs of X-ray irradiation contributes no major variation in the degree of damage.

Boron Ion Interaction with pnp Bipolar Power Transistor and Displacement Damage Effects on its Electrical Characteristics

Bipolar junction transistors used in switching and amplification applications is examined for their electrical performance after irradiation with 60 MeV boron ions of different fluence. Unirradiated device base current is 5.97×10-5 A while it is 9.03×10-4 A after irradiation with a fluence of 1×1012 ions/cm2. For unirradiated device collector current is 1.22×10-3 A and is 7.31×10-4 A after irradiation to a fluence of 1×1012 ions/cm2. Base current increases whereas collector current decreases after irradiation with a fluence of 1×1012 ions/cm2. The magnitude of decrease in collector current is approximately same as that of the increase in base current, showing the leakage of the collector current due to irradiation. The output collector gain of the unirradiated transistor is 20.5 after irradiation to a fluence of 1×1012 ions/cm2 it has reduced to 0.81. The capacitance measurements for base-emitter junction show that for the unirradiated and irradiated samples, linearity of the curves indicate uniformity of shallow doping concentration. The built in potential (Vbi) for unirradiated device is 2.69V and after irradiation it is 2.52V. The device is also studied for activation energy, trap concentration and capture cross-section of deep levels are studied using deep-level transient spectroscopy (DLTS) technique. Majority carrier trap level is observed with energy Ev+0.784eV.

Dose rate dependence of radiation-induced lattice defects and performance degradation in npn Si bipolar transistors by 2-MeV electron irradiation

Total-dose response of npn Si transistors by 2-MeV electrons is presented for different dose rates. The base current increases after irradiation, whereas the collector current decreases. Therefore, the current gain ( β) decreases by irradiation. The degradation of electrical properties by 2-MeV electrons for low dose rate is higher than that for high dose rate. Similar dose rate dependence of the radiation-induced electron trap densities is observed by deep-level transient spectroscopy (DLTS) measurements.

High-energy electron induced gain degradation in bipolar junction transistors

This paper describes the effect of 8MeV electron beam on the forward current gain of space borne commercial indigenous bipolar junction transistors 2N2219A (npn), 2N3019 (npn) and 2N2905A (pnp). The devices are exposed to 8MeV electron in the biased condition. The collector characteristics and Gummel plots are obtained as a function of accumulated dose. An excess base current model as well as Messenger–Spratt equation have been used to account for the observed gain degradation. The results indicate that 8MeV electrons of high dose rate induce gain degradation by increasing the base current as well as decrease in collector current. The current gain degradation appears to be predominantly due to displacement damage in the bulk of the transistor. Off-line measurements of the hFE of the irradiated transistors indicate that the displacement induced defect and recombination centers do not anneal even at 150°C.

Sulfur and low-temperature SiNx passivation of self-aligned graded-base InGaAs/InP heterostructure bipolar transistors

The passivation of self-aligned InGaAs/InP heterostructure bipolar transistors (HBTs) with graded base by the combination of S and low-temperature deposited SiNx was investigated. Base current was found to decrease after the passivation. Collector current significantly increases at low base-emitter voltages. The increase is attributed to the leakage current of the base-collector diode. The current gain was found to increase. When annealing was performed at 300 °C for 5 min, the base current decreases further and the collector current decreases. The leakage of collector current was found to be suppressed. The current gain was further improved and the leakage current can affect the Gummel plots. The leakage source was identified to be the interface between the semiconductor and the SiNx layer. The leakage current can be decreased by the annealing process.

Model for the decrease in HBT collector current under DC stress based on recombination enhanced defect reactions

Based on simplifying assumptions a model is developed to describe decreasing HBT collector current under DC bias stress. The underlying processes are recombination enhanced defect reactions (REDR), namely defect generation and defect annealing. The simplification of the derived equation under particular boundary conditions leads to a form of the Eyring relationship generally employed to describe the decrease in collector current under DC bias stress. Additionally, pulsed tests with an emitter current density of JE=200 kA/cm2 have been performed. The comparison between measured data from these tests and their fit proofs the applicability of the derived equation. Of course this can not be an evidence for the real running physical processes.

Degradation of DC characteristics of InGaAs/InP single heterojunction bipolar transistors under electron irradiation

The effects of high-energy (/spl sim/1 MeV) electron irradiation on the dc characteristics of InGaAs/InP single heterojunction bipolar transistors (SHBT's) are investigated. The device characteristics do not show any significant change for electron doses <10/sup 15//cm/sup 2/. For higher doses, devices show a decrease in collector current, a degradation of common-emitter current gain, an increase in collector saturation voltage and an increase in the collector output conductance. A simple SPICE-like device model is developed to describe the dc characteristics of SHBT's. The model parameters extracted from the measured dc characteristics of the devices before and after irradiation are used to get an insight into the physical mechanisms responsible for the degradation of the devices.

Degradation of InGaAs/InP single heterojunction bipolar transistors under high energy electron irradiation

Abstract The d.c. characteristics of InGaAs/InP single heterojunction bipolar transistors (SHBTs) were studied for the first time under high energy (∼1 MeV) electron radiation of cumulative dose up to 5.4×1015 electrons/cm2. No degradation was observed for electron doses below 1015/cm2. For electron doses greater than 1015/cm2 the following degradation effects were observed: (1) decrease in collector current; (2) decrease in current gain up to 50%; (3) an increase in collector saturation voltage by 0.2–0.8 V depending on base current; and (4) increase in output conductance. The degradation of collector current and current gain are thought to be due to increased recombination caused by radiation-induced defects in the base–emitter junction. The increase in collector saturation voltage is attributed to an increase in emitter contact resistance after irradiation. The increase in the avalanche multiplication in the reverse biased base–collector junction caused by radiation induced defects is believed to be responsible for increased output conductance after irradiation.

Radiation-induced gain degradation in lateral PNP BJTs with lightly and heavily doped emitters

Radiation-induced gain degradation is compared in two types of lateral PNP bipolar devices that are identical except for the emitter doping. The devices with heavily-doped emitters (1/spl times/10/sup 20/ cm/sup -3/) degrade less than the devices with lightly-doped emitters (1/spl times/10/sup 18/ cm/sup -3/). Both device types are sensitive to interface-trap formation in the oxide above the emitter-base junction and the neutral base region. In addition, the devices with lightly-doped emitters experience spreading of the depletion region into the emitter, increasing their sensitivity to total-dose irradiation. The gain degradation in both device types is due to a combination of increased base current and decreased collector current. The radiation-induced decrease in collector current is more significant for devices from this technology than for other devices studied previously. Increased gain degradation is observed in heavily-doped devices irradiated at low dose rates, but the enhanced degradation appears to be due to time-dependent effects rather than true dose-rate effects. The lightly-doped devices do not exhibit a clear dose-rate trend and the gain of these devices improves during post-irradiation annealing.

Technique for measurement of the minority carrier mobility with a bipolar junction transistor

A simple technique to measure the minority carrier mobility using a bipolar junction transistor is demonstrated. By fixing the base-emitter voltage, the carrier injection into the base is constant. The collector current is then monitored as a function of a magnetic field applied perpendicular to the current transport across the base. The magnetic field leads to an increase in base transit time and a corresponding decrease in collector current. From the resulting fractional change in collector current, the minority carrier mobility in the base can be determined. For narrow base transistors, quasiballistic transport across the base must be taken into account when determining the bulk minority carrier mobility.

Fabrication of a platinum dual-disk microelectrode and investigation of its properties

Platinum dual-disk microelectrodes with interelectrode gaps of 5–40 μm were constructed for the first time by fixing two 60 μm diameter platinum wires onto a glass slide with epoxy resin as a fixative. The collection efficiency, shielding and feedback factors were investigated in detail. The collection efficiency is related both to the geometry gap width and the method used to polish the electrode and increases with a decrease of the gap width. The collection efficiency for a dual-disk microelectrode with a gap of 5 μm is 44.4%. The collector current decreases with an increase of the concentration of the ascorbic acid added to the solution of 2.0mmoll 1 K 4Fe(CN) 6, because the follow-up chemical reaction between Fe(CN) 6 3 and the ascorbic acid causes a decrease of the concentration of Fe(CN) 6 3 diffusing to the collector. Shielding and feedback factors of this device are very small. The fluctuation of the collector current was observed due to the influence of the natural convection or vibration. The effects of temperature and stirring were also discussed. Results show that both the temperature and stirring result in an increase of the generator current. However, the collector current rises with the temperature and falls rapidly with an increase of the stirring rate.

Total inelastic cross sections for slow electrons in xenon†

An electron beam of low energy enters a cubic wire gauze chamber in Xe at a pressure of about 10−2 torr. The scattered electrons escaping from the chamber are received by a collector kept at a retarding potential of frac13; of the accelerating voltage. When inelastic collisions duo to excitation sot in, the collector current decreases. In order to derive from this change the absolute cross section, the average number of electron collisions in the chamber must be known; this was determined in two ways. With this result and the observed variation of the collector current with the accelerating voltage the total excitation cross section is found between the lowest excitation potential of 8-2 v and the ionization potential of 12-1 v; multiple scattering, energy spread and closeness of energy levels of Xe prevent the appearance of a fine structure. For energies up to 15 v approximate cross-section values are obtained after allowing for the positive ion current and including the known ionization cross sections. Further analysis of the results suggests that the transparency of the gauze is smaller than its geometric value, that it varies with the energy of the electrons and positive ions and that the ion concentration in the chamber is relatively large. The electron emission from the collector by Xe ions and metastable atoms seems to be insignificant.