Minority-carrier Transit Time Research Articles

Novel approximative analytical expressions for minority-carrier transit time including recombination

A novel analytical model for the minority-carrier transit time has been developed including the recombination effects. It has been found that the recombination effects substantially influence transit time in quasi-neutral regions with low effective contact recombination velocities and/or low minority-carrier diffusion length. In these cases, the difference of charge control concept transit time and the basic transit time definition have been analysed.

InGaAs PIN photodiodes on semi-insulating InP substrates with bandwidth exceeding 14 GHz

The top-illuminated InGaAs PIN photodiodes have been fabricated from materials grown by metalorganic vapor phase epitaxy. Using the planar air-bridge approach and the selective etching technique, it can eliminate the significant bondpad capacitance which is present in conventional PIN photodiodes on conducting substrates. Besides, a self-aligned lift-off process is used for the n-contact recess and metallization. The anti-reflection coating devices have responsivity of 0.79 and 0.78 A/W at 1.3 and 1.55 μm, respectively. The fabricated devices with 30 μm photosensitive diameter have a very low dark current below 0.2 nA and low capacitance of 143 fF at −5V bias voltage. The 3-dB bandwidth of these devices is in excess of 14.8 GHz which is in good agreement with the calculated minority-carrier transit time through an absorbing layer thickness of 1.85 μm. The device performance reveals that these devices are potentially suitable for the applications in optoelectronic integrated circuits.

A temporally resolved position sensing device for autofocusing

A position-sensing method for autofocus purpose is demonstrated, based on the triangular ranging principle applied to a photoconductive Haynes–Shockley device. This method provides a linear variation of the minority-carrier transit time in the sensor with respect to the inverse of the object distance, or to the image distance to be adjusted from the focal point. Hence it can provide a convenient autofocusing control with a fully digital signal processing circuit. The principle of the autofocus triangular ranging is justified, and its resolution is analyzed with a p-type silicon photoconductor. The result shows that our method indeed can provide a high resolution and practically low cost autofocusing device for the camera industry.

Time-of-flight studies of minority-carrier diffusion in AlxGa1−xAs homojunctions

A novel time-of-flight technique has been developed for simultaneously measuring minority-carrier lifetime and diffusivity in homojunctions. A pulsed dye laser produces electron-hole pairs near the front surface of the device. A delay occurs before the onset of photocurrent due to the diffusion transit time of minority carriers to the junction. An analysis of this effect by both a simplified analytical model and a computer simulation gives similar results for the current as a function of time. A fit of the theory to experimental data on Al0.25Ga0.75As n/p homojunctions produces minority-carrier lifetime, diffusivity, and diffusion length.

Transit time and charge storage measurements in heavily doped emitters

We report results of a first direct measurement of the minority-carrier transit time in a transparent heavily doped emitter layer. The value was obtained by a high-frequency conductance method recently developed and used for low-doped Si. The transit time coupled with the steady-state current enables the determination of the quasi-static charge stored in the emitter and the quasi-static emitter capacitance. Using a transport model, we estimated, from the measured transit time, the value for the minority-carrier diffusion coefficient and mobility. The measurements were done using a heavily doped emitter of the Si p+-n-p bipolar transistor. The new result indicates that the position-averaged minority-carrier diffusion coefficients may be much smaller than the corresponding majority-carrier values for emitters having a concentration ranging from about 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> .

Minority-carrier diffusion coefficients and mobilities in silicon

A new method for accurate measurement of minority-carrier diffusion coefficients in silicon is described. The method is based on a direct measurement of the minority-carrier transit time through a narrow region of the p-n junction diode. The minority-carrier mobility is obtained from the diffusion coefficient using the Einstein relation. The method is demonstrated on low-doped n- and -p-type Si (dopings ∼10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) and is compared with the literature data for the majority-carrier mobilities. The results show that in low-doped Si the electron minority- and -majority-carrier mobilities are comparable, but the hole minority-carrier mobility is significantly higher (∼30 percent) than the corresponding majority-carrier value. The results confirm earlier data of Dziewior and Silber.

Transit time studies of junction location in thin-film solar cells

The active junction in Cd(Zn)S/CuInSe2 thin-film solar cells was investigated by a pulse photoconductivity technique. We observed the diffusion transit time of minority carriers to a homojunction internal to the CuInSe2. No electrical activity at the heterojunction was indicated.

Graded-band-gap pGa1−xAlxAs-nGaAs heterojunction solar cells

The theoretical spectral response of the graded-band-gap pGa1−xAlxAs-nGaAs solar cell is calculated by solving the continuity equations. The electric fields produce a collection efficiency two times larger than that of the abrupt heterojunction diodes at wavelengths less than 700 nm for surface recombination velocities of 106–107 cm/sec. The graded-band-gap diode can be operated at high frequencies because of the reduced transit time of minority carriers in the p-type layer. A graded-band-gap pGa1−xAlxAs-nGaAs solar cell is fabricated by utilizing the diffusion of Al in the Ga melt. The gradient of the energy gap is evaluated by photoresponse and photoluminescence measurements. The photoluminescence shows a broad emission peak from 700 to 800 nm at 77 K.

A Simple Transistor Neutron Hardness Screen Using Scattering Parameters

A frequency domain model of the common emitter S21 parameter of a junction transistor is derived which includes the effect of minority carrier transit time through the active device. Using this model it is demonstrated that the minority carrier transit time can be measured using scattering parameters. S-parameter derived transit time is used to predict neutron induced gain degradation. A prediction accuracy of approximately 5% is demonstrated.

High-frequency physical equivalent circuit of junction transistors in common collector configurationt

Abstract New high-frequency equivalent circuits derived from physical theory have been recently proposed for common-emitter and common-base operations. The analysis is now extended to provide a high-frequency physical equivalent circuit for the common-collector operation. All the constants of the ' intrinsic transistor ' are expressed as simple functions of one or more of just three physical parameters of the transistor, viz. the base region lifetime, minority carrier transit time in the base and a dimensionless basewidth modulation parameter, A, apart from the quiescent currents in the three leadB of the transistor.

Analysis of Transistor Mixer for Large Local Oscillator Drives

A conventional transistor mixer is analysed for large local oscillator drives. Its conversion conductance is expressed in terms of minority carrier transit time, oscillator crest voltage and the emitter direct current. This analysis is valid for a wide range of emitter direct current and oscillator voltage, provided that the oscillator and signal frequencies are small compared with the ft of the transistor.

Transient Double Injection in Semiconductors with Traps

Deep traps can have important effects on the transient behavior of an electron-hole plasma injected into a long semiconductor. If the minority-carrier transit time is much shorter than all capture times (high voltage), trapping effects modify the trap-free transient after the first transit time by stretching out the transient and increasing the steady-state current. If the minority-carrier transit time is longer than the initial minority-carrier trapping time but shorter than all other capture times (intermediate voltage), trapping effects enter immediately. They reduce the velocity of the propagating plasma and cause the current to exhibit a long delay followed by a sharp rise. When the applied voltage is decreased further, the plasma velocity drops sharply toward zero because of recombination through the trapping centers. Properties for a typical bar of p-type InSb at liquid-nitrogen temperature are inserted in the appropriate formulas, and the results agree qualitatively with experimental data in the literature.

Approximations to α for diffusion transistors

The paper reviews, from the viewpoint of design engineers, various approximations to the common-base intrinsic current gain of junction transistors. The basis of this comparison is the familiar expression for α derived directly from the semiconductor diffusion and continuity equations.A 2-pole approximation is considered in detail. It is shown that both the sinusoidal and transient response predicted using this expression is in good agreement with that predicted using the exact theory. For most practical transistors the parameters of this approximation remain reasonably constant.In the response to a step function of emitter current, the 2-pole equation closely describes the initial time delay arising from the transit time of minority carriers across the base region. The collector response to unit charge inserted into the base in the form of σ function also gives good agreement with the results obtained from the exact theory.The various approximations are compared by graphical presentation of the results.

The Frequency Response of Bipolar Transistors with Drift Fields

The frequency response of bipolar transistors is calculated using a model which assumes that the spread in the transit time of minority carriers flowing from emitter to collector is the major factor in determining the frequency cutoff. The total emitter-to-collector transit time is determined by the combined effects of drift and diffusion but the spread in transit time is determined exclusively by diffusion. The analysis is adapted to point-contact transistors and checks experimental measurements of frequency cutoff in four groups of point-contact transistors having different structure and material parameters.