Internal Current Gain Research Articles

Multiple-quantum-well-induced unipolar carrier transport multiplication in AlGaN solar-blind ultraviolet photodiode

AlGaN solar-blind ultraviolet (SBUV) detectors have potential application in fire monitoring, corona discharge monitoring, or biological imaging. With the promotion of application requirements, there is an urgent demand for developing a high-performance vertical detector that can work at low bias or even zero bias. In this work, we have introduced a photoconductive gain mechanism into a vertical AlGaN SBUV detector and successfully realized it in a p - i - n photodiode via inserting a multiple-quantum-well (MQW) into the depletion region. The MQW plays the role of trapping holes and increasing carrier lifetime due to its strong hole confinement effect and quantum confinement Stark effect. Hence, the electrons can go through the detector multiple times, inducing unipolar carrier transport multiplication. Experimentally, an AlGaN SBUV detector with a zero-bias peak responsivity of about 0.425 A/W at 233 nm is achieved, corresponding to an external quantum efficiency of 226%, indicating the existence of internal current gain. When compared with the device without MQW structure, the gain is estimated to be about 10 3 in magnitude. The investigation provides an alternative and effective approach to obtain high current gain in vertical AlGaN SBUV detectors at zero bias.

Hybrid Graphene/Cu2O Quantum Dot Photodetectors with Ultrahigh Responsivity

AbstractFlexible high‐sensitivity photodetectors are desirable for use in future wearable optoelectronics. Graphene is attracting considerable attention because of its outstanding electrical, optical, and mechanical properties, which make graphene appealing in flexible optoelectronics and photodetection applications. In this paper, an internal current gain mechanism is proposed based on a 2D/0D photodetection system. The carrier density in the 2D material can be amplified via Fermi level modulation when a 0D quantum dot absorbs photons. An ultrahigh responsivity of more than 1010 A W−1 and fW‐scale light detectivity are achieved at room temperature using the flexible transfer‐free hybrid graphene/Cu2O quantum dot photodetector developed in this work. After excessive bending, the responsivity of the photodetector still reaches 106 A W−1, thus demonstrating the promising flexibility of the device.

Turn-ON Analysis for a Thyristor-Based Photoreceiver

An analysis of the turn-ON time for a thyristor-based photoreceiver is presented. Using an equivalent circuit that incorporates internal bipolar current gain, the time to trigger and switch the detector on is quantified analytically. For typical device parameters and applying values of photocurrent gain obtained from experimental data, turn-ON times on the order of 25 ps are predicted for a $10~\mu \text{m}$ device diameter.

Optically Activated SiC Power Transistors for Pulsed-Power Application

To realize the benefits of SiC power electronics and optical-driving device technology, we present optically activated SiC power transistors for pulsed-power application. Although limited by the indirect bandgap of SiC, the transistor employs a bipolar structure with an internal current gain, which amplifies the photogenerated current and therefore has the capability to reduce the optical-triggering power requirement. The transistors are fabricated on an n-type 4H-SiC substrate with switch-on triggered by a short UV (337.1 nm) laser pulse with 0.5-mJ optical energy. The transistor successfully switches 1200 V with an FWHM of about 180 ns, a rise time of less than 20 ns, and a fall time of about 200 ns. This initial work forms the basis for the further development of high-speed and energy-efficient SiC-based optically controlled power switches for high-temperature and high-power applications.

Punch through float-zone silicon phototransistors with high linearity and sensitivity

In this paper, we propose, analyze and demonstrate a high-purity float-zone (FZ) silicon phototransistor operating at the punch through state with high linearity and sensitivity. Those phototransistors were fabricated on high-purity FZ silicon substrates; the dependence of the sensitivity on incident optical power and bias voltages has been investigated to light with a wavelength of 0.83 μm from a laser diode. In accordance with theoretical prediction, it shows that the linearity reaches the highest when the base of the phototransistor is completely depleted (punch through), and the fitting goodness of output R 2 is 0.9954 over a 40 dB range from 0.15 to 1500 nW. The sensitivity of the phototransistor can be as large as 40–70 A/W at the punch through state, which is equivalent to an internal current conversion gain of about 75–130. The stability of 1% in the sensitivity for the punch through phototransistor with an internal current conversion gain of 130 can be obtained if the bias voltage and operating temperature can be stable to about 2.5% (1 in 40 V) and the temperature to ±2 °C.

A novel photodetector with new internal gain and short response time

A new type of photodetector with specific properties is introduced in this paper. Its output characteristics differ greatly from those of ordinary photoelectric transistors. When it works in the peak region, the response time is very short and it produces a new internal current gain. This suggests that there are good prospects for extensive applications in the future.

On the internal current gain of buried N-body silicon-on-insulator N-metal-oxide-semiconductor field-effect-transistors

We give a simplified expression of the internal current gain of buried N-body silicon-on-insulator N-metal-oxide-semiconductor field-effect-transistors. It applies only for the subthreshold region of operation, which is required for the bipolar action. The existence of a body effect is emphasized and explains the change of the current gain versus the body doping and the silicon film thickness. For a more accurate estimate of the current gain, it would be required to account for space charge hole recombination and high injection effect.

Noise and dynamical gain studies of GaAs photoconductive detectors

Noise measurements on N-type GaAs planar photoconductive detectors have been made over the 10 MHz–1.5 GHz frequency range. The dynamical gains of the devices were calculated from noise data and compared with the values obtained using picosecond measurements. In the gigahertz frequency domain, the photodetectors have an internal current gain as observed in the avalanche photodiodes, but no excess noise factor has been found.

New method of measuring the internal current gain of a transistor using avalanche multiplication

A new method is proposed which measures the emitter efficiency of a transistor when the emitter current is pinched in at the middle of the emitter. The measurement is then not confused by the effects of the edge of the emitter-base junction. The technique uses the charge carriers generated by avalanche multiplication in the collector-base junction to create this pinch-in condition. Measurement of external parameters such as emitter current, external base current, and collector voltage are then shown to yield the emitter efficiency provided recombination in the base is negligible.

High-gain wide-gap-emitter Ga 1 - x Al x As-GaAs phototransistor

A Ga1-xAlxAs-GaAs heterostructure phototransistor has been manufactured and tested. The device is an n-p-n structure employing the ‘wide-gap-emitter’ effect. High internal current gain (>2000) has been achieved.

Photoresponse of the GaAs controlled field avalanche photodiode (CFAPD)

A GaAs metal-semi-insulating-p-n+ avalanche photodiode has been evaluated as photodetector in current gain and spectral response. The influence of deep chromium levels on the behavior of the device in the semi-insulating region has been taken into account. A donor level at 0.56 eV and an acceptor level at 0.93 eV from the conduction band have been detected by photocurrent and photocapacitance measurements. An internal current gain, due to avalanche multiplication higher than 104, has been obtained. Spectral response is extended up to 1.61 μm.

Sensitive high speed photodetectors for the demodulation of visible and near infrared light

Photomultipliers, solid state photodiodes and avalanche photodiodes are the preferred detectors for the demodulation of light intensity variations at visible and near infrared wavelengths. The principles of operation of these detectors will be described together with their basic construction and operational characteristics. Photomultipliers with the recently developed high efficiency photocathodes for visible and near infrared wavelengths and the high gain dynode arrangements with fast speed of response will be mentioned. The various types of silicon and germanium photodiodes with and without internal current gain will be discussed. Tradeoffs involved in the optimization of quantum efficiency, speed of response, internal current gain and sensitivity to weak light signals will be treated in detail for silicon photodiodes operating at wavelengths either in the visible or at the GaAs (≈0.7–0.9 μm) or YAG (1.06 μm) infrared laser emission lines. The capabilities of germanium avalanche photodiodes for the detection of infrared light at wavelengths up to about 1.6 μm will be mentioned.

Photodetectors for optical communication systems

The characteristics of high-sensitivity photodetectors suitable for wide bandwidth optical communication systems are summarized. Photodiodes, photomultipliers, and photoconductive detectors for wavelengths from 0.3 µm to 10.6 µm are covered. The use of internal current gain by means of avalanche and electron multiplication and by means of optical heterodyne detection to increase sensitivity of high speed photodetectors is discussed. The application to visible and infrared laser communication systems is reviewed.

Internal current gain in microwave-biased gallium-doped silicon 8-14 µm IR detectors

It has been shown that internal current gain may be obtained by the application of microwave bias to intrinsic photoconductors. This letter presents experimental evidence of the same effect in an extrinsic photoconductor, gallium-doped silicon.

High-Speed Photodetectors

This paper is intended as a status report on high-speed detectors for the visible and near-infrared portion of the optical spectrum. Both vacuum and solid-state detectors are discussed, with the emphasis on those devices which can be used as direct (noncoherent) detectors of weak optical signals modulated at microwave frequencies. The best detectors for this application have internal current gain and in this regard the relevant properties and limitations of high-frequency secondary emission multiplication in vacuum tube devices and avalanche multiplication in p-n junctions are summarized.

High-speed photodetectors

This paper is intended as a status report on high-speed detectors for the visible and near-infrared portion of the optical spectrum. Both vacuum and solid-state detectors are discussed, with the emphasis on those devices which can be used as direct (noncoherent) detectors of weak optical signals modulated at microwave frequencies. The best detectors for this application have internal current gain and in this regard the relevant properties and limitations of high-frequency secondary emission multiplication in vacuum tube devices and avalanche multiplication in p-n junctions are summarized.

An investigation of the current gain of a drift transistor at frequencies up to 105 Mc/s

The complex internal short-circuit current gain, αd, of a type 2N247 plane alloy-junction germanium transistor has been determined from measurements of the external short-circuit current gain, by taking account of the effects of the emitter and collector depletion-layer capacitances and the ohmic base resistance. Measurements have been made up to 105 Mc/s and over a range of emitter current from 50 μA to 8 mA. It has been found that the loci of αd may be interpreted in terms of Kroemer's theoretical treatment, which is based on the existence of a uniform drift field across the base. The value of ΔV/kT is found to be 5 at room temperature.

An investigation of the dependence of the current gain of a plane-alloy-junction transistor on emitter current and frequency

The complex internal current gain, αd, of a diffusion-type germanium transistor has been derived from measurements of the external short-circuit current gain, α, at frequencies up to 20 Mc/s and for emitter currents between 15 μA and 3 mA, by taking account of the effects of the emitter and collector depletion-layer capacitances and the ohmic base resistance. The resulting frequency dependence of αd is that expected from unidimensional diffusion theory. At low emitter currents, the flow of r.f. current in the emitter depletion-layer capacitance causes the cut-off frequency of α to be less than one-third that of αd.

The current gains of diffusion and drift types of junction transistors

Theoretical aspects of the frequency dependence of current gain are reviewed. A semi-empirical expression for the common-base internal current gain αd is given, which closely approximates to the theoretical expression and is useful for analytical work.Measurements of the complex common-base external current gain α, from which αd is derived, are presented for frequencies up to 210 Mc/s. A comparison of the complex loci of αd with theoretical loci shows good agreement in most cases. A simple method of estimating the relative drift potential across the base of drift transistors is discussed, and two methods of determining the emitter depletion-layer capacitance are described.

An investigation of the current gain of transistors at frequencies up to 105 Mc/s

Apparatus is described by means of which the short-circuit current gain is measured directly. Results of such measurements are presented for commercial alloy-junction and surface-barrier transistors; corrections are applied to yield the internal diffusion-current gain. The effects of stray capacitances on the measurements are discussed. The cut-off frequency of the internal current gain is compared with values derived indirectly from other measurements. For alloy-junction transistors the behaviour is closely in accord with existing one-dimensional diffusion theory, with some reservations, but for surface-barrier transistors the agreement is less close.