Effect Of Carrier Diffusion Research Articles

An analytic model for the modulation response of buried heterostructure lasers

This paper describes an analytic model for the modulation response of buried heterostructure (BH) semiconductor lasers. Using a space-averaged carrier density approach, explicit expressions that take into account the combined effects of carrier diffusion and spontaneous emission are derived for the transient decay time of the relaxation oscillations, and the small-signal modulation response for the carriers and photons. The dynamic shift of the lasing wavelength is estimated by calculating the fluctuations of the carrier density during small-signal modulation. Using the analytic solutions obtained, a network synthesis approach is used to derive two-port circuit models for the device. The validity of the theoretical model is verified by comparing the modulation characteristics of a BH laser measured experimentally to that simulated by circuit analysis.

Amplification of Bleustein–Gulyaev waves in cadmium sulfide

The propagation of Bleustein–Gulyaev waves in the presence of a dc electric field in the vacuum baked piezoelectric semiconducting crystals of class 6 has been studied theoretically. By solving the partial differential equations representing the electron–acoustic wave interaction in the piezoelectric semiconducting region, and the Laplace’s equation in the vacuum region separately and fulfilling the relevant boundary conditions, we obtain an expression for the amplification coefficient. The effects of carrier diffusion, resistivity, and carrier drift velocity on the amplification coefficient have been studied based on numerical calculations for the semiconducting CdS sample. It has been observed that, compared to Rayleigh waves, the Bleustein–Gulyaev waves give a much higher amplification.

Measurement of the low energy tail spectra adjacent to the x-ray photopeak in Si(Li) x-ray detectors

Low energy tail spectra, which are inherently observed adjacent to the X-ray photopeak in the use of a Si(Li) X-ray detector, have been measured for the 1.3–3.7 keV X-ray energy range. Three different Si(Li) detectors have been tested. The tail/peak count ratios as a function of incident X-ray energy have exhibited a rapid change at the boundary energy of the Si K absorption edge. From the observed tail/peak count ratios, the thickness of the Si layer which produces the tail spectrum has been estimated; the thicknesses for the three tested detectors are about 0.05, 0.1 and 0.2 μm. In addition to the carrier diffusion effect, it is proposed in the case of a Si(Li) detector that the effect of the escape (penetration) of Auger and phtoelectrons from (into) the intrinsic region plays an important role in the production of the tail spectra.

Effects of ambipolar excess carrier diffusion in pulsed laser annealing of semiconductors

Effects of ambipolar excess carrier diffusion in pulsed laser annealing of semiconductors

MTF modelling of backside-illuminated PV detector arrays

Backside-illuminated detector arrays are used extensively in hybrid focal plane arrays. The MTF of the detector array is affected by the cross-diffusion of photo-generated carriers, especially for materials with long diffusion lengths such as HgCdTe. In this paper, the MTF of the backside-illuminated detector arrays, including the effect of carrier diffusion, are modelled. The MTFs are calculated as a function of detector thickness, absorption coefficient, pixel size and diffusion length. The trade-off of detector MTF and quantum efficiency is also analyzed.

The effect of lateral carrier diffusion on the modulation response of a semiconductor laser

The effect of lateral carrier diffusion upon the modulation characteristics of the semiconductor laser is investigated. A self-consistent analysis of the spatially dependent rate equations is performed using a finite element model. The transverse junction stripe laser is treated as an example and a comparison is made between lateral carrier diffusion and spontaneous emission as damping mechanisms for the resonance peak. Experimental results bear out the conclusion that the relaxation resonance in this device is damped mainly by lateral carrier diffusion. In addition, a simple analytic result is presented which illustrates qualitatively the effect of lateral carrier diffusion upon such devices. The conclusion from this result is that lateral carrier diffusion serves to damp the relaxation resonance in the semiconductor laser quite well, but probably will not serve to improve the upper limit on modulation frequency as might have been suspected.

A novel heterostructure interdigital photodetector (HIP) with picosecond optical response

The demonstration of a novel and simple heterostructure interdigital photodetector (HIP) is reported. The detector displays 50- 60 ps symmetric rise and fall times, low operating voltages (∼10-25V), with a dc responsivity greater than 0.3 A/W at λ = 0.83 µm. The results obtained are comparable to the fastest commercial high speed detectors available today. The device is compatible with planar technology and thus should lend itself to integration with MESFET's or other microwave integrated circuits. Lastly, the concept of using a heterostructure to confine the injected carriers should ultimately provide high speed operation by limiting the detrimental effects of carrier diffusion and traps in the semi-insulating substrate.

Laser heating of semiconductors—effect of carrier diffusion in nonlinear dynamic heat transport process

An analytic theory is presented to describe the nonlinear dynamic heat transport process in a semiconductor irradiated by a pulsed laser beam. The input rate of laser energy to the lattice is sensitively influenced by the ambipolar diffusion of the dense, laser-produced excess charge carriers. Additionally, the high heating rate of the laser beam significantly changes the material transport coefficients during the pulse. This nonlinear laser beam-solid interaction is examined from the viewpoint of the transport process, using a parametrized perturbation technique in Green′s function formulation. An explicit, analytical solution of the lattice temperature rise is presented and the threshold pulse energy for the onset of surface melting for the case of amorphous Si is calculated as a function of laser beam intensity as well as the carrier diffusion length. Our results are compared with both the melting and nonthermal models for laser annealing.

Final comments on "Effects of carrier diffusion on the small-signal performance of IMPATT diodes"

Final comments on "Effects of carrier diffusion on the small-signal performance of IMPATT diodes"

Final comments on "Effects of carrier diffusion on the small-signal behavior of IMPATT diodes"

Final comments on "Effects of carrier diffusion on the small-signal behavior of IMPATT diodes"

Further comments on "Effects of carrier diffusion on the smal1-signal behavior of IMPATT diodes"

Further comments on "Effects of carrier diffusion on the smal1-signal behavior of IMPATT diodes"

The effect of carrier diffusion on laser heating of lightly damaged semiconductors

It has been observed that the surface temperature obtained during laser heating of lightly damaged material is generally considerably lower than the temperature obtained in heavily damaged material. We develop a model which explains this observation by taking into acount the diffusion of the photoexcited carriers. The time evolution of temperature profiles was calculated for pulsed ruby and Nd : YAG illumination of silicon and ruby illumination of GaAs. The material, optical, and electronic properties were varied, according to the material quality. Surface recombination of the carriers was also taken into account. For the same laser power, the induced temperature was lower and the heating times were longer in good-quality materials than in heavily damaged materials. This is because of longer carrier difusion lengths in good-quality material. The effect of the damage on the heating was found to be much more pronounced for Nd : YAG than for ruby irradiation because a larger portion of the ruby laser energy (excess above band gap) is given rapidly to the lattice through quasithermalization inside the semiconductor energy bands. Thermal spikes are formed as the result of the preferential recombination of the carriers at the surface. For a sufficiently fast surface recombination, the temperature profile may develop a secondary maximum in the material interior.

Comments on "Effects of carrier diffusion on the small-signal behavior of IMPATT diodes"

The above paper presented computed results for the effects of carrier diffusion on the small-signal behavior of avalanche diodes. It is suggested that these results be treated with caution, since the equations solved are not those normally associated with the problems under consideration. Other aspects of the paper <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> which could be misleading are also indicated.

Effect of carrier diffusion on the small-signal behavior of IMPATT diodes

An approach to the detailed computer simulation of dc and small-signal IMPATT behavior is described in which allowance is made for carrier-diffusion effects. Results are presented for a variety of structures in Si and GaAs, including high-efficiency structures using the latter material. The results from the simulation are also compared with the predictions of a quasi-static theory for a particular case, and good general agreement is observed.

Transfer of on states between closely spaced negative-resistance p+-i-n+diodes

The possibility of making a shift register using an array of p+-i-n+diodes has been examined by investigating the transfer action of the on state of negative resistance characteristics between closely spaced p+-i-n+diodes. A gold-doped Si substrate is used to fabricate the p+-i-n+ structure. The possibility of the transfer of the on state has been examined. The main requirements for transferring are as follows: (a) The array of diodes must be located within about 500 µm in lateral length, (b) The operation time of the transfer action must be within about 10 µs. To clarify the transfer mechanism, experiments concerning the effect of carrier diffusion, Joule heat and recombination radiation due to on state current from one diode to the adjacent diode have been carried out. From the experimental results, it has been found that the transfer mechanism is dominated by carrier diffusion from the filamentary current path of one diode to the next.

A simple approximate method of estimating the effect of carrier diffusion in IMPATT diodes

Most large-signal analyses of IMPATT diodes neglect the diffusion of charge carriers in the drift region. A correction can be introduced to include the effect of diffusion in the negative conductance or the efficiency of the IMPATT diode calculated from such analyses. An approximate method of estimating a simple correction factor is presented using the Read model of the diode.

Effect of mobile carrier diffusion and its treatment in simulation programs for p-i-n switches and limiters

Effect of mobile carrier diffusion and its treatment in simulation programs for p-i-n switches and limiters

Effect of carrier diffusion on operation of avalanche diodes

The effect of carrier diffusion on the performance of avalanche diodes has received little attention in the literature. This letter presents a simple analytical model of the effects of diffusion on device performance, and arrives at an upper frequency limit dictated by the diffusion effect. The model can be used to give a derating factor onto analyses that neglect this parameter. An example of the application of this is given, and the results compared with previously published computer simulations.

Small-signal design theory and experiment for the punch-through injection transit-time oscillator

The small-signal theory of the punch-through ‘barrier-injection and transit-time’ (BARITT) diode is given and the physical mechanisms of device operation are described. Both velocity modulation and charge density modulation components of current are included and the effects of carrier diffusion in the source regions of the device are taken into account by using an equivalent small-signal conductivity for the potential barrier which controls charge injection. It is shown how carrier bunching in the source regions creates space-charge waves which propagate through the source-drain space and generate power as the associated component of current moves into anti-phase with the local electric field. Theoretical curves are presented for a typical PNP silicon device and agree well with experimental measurements of series resistance and series capacitance. A device of area 1·25 × 10 −8 m 2 (5 thou. diameter) and source to drain spacing of 5 μm made in 5 Ω cm material was found to possess negative resistance over the wide frequency range from about 5 GHz to about 12 GHz with a maximum value of about — 5 Ω.

Small-signal theory of transit-time diodes

Transit-time diodes, in which the effects of carrier diffusion and generation or recombination are not important, have recently been investigated both theoretically and experimentally. The impedance of these devices, mainly due to one type of carriers, has been computed by several authors with different simplifying assumptions. In this paper a more general expression of the impedance of the transit-time diode is given, accounting for the spatial non-uniform d.c. distributions of the electric field and of the carrier velocity, and by allowing any dependance of the carrier mobility on the d.c. electric field. The impedance is given in closed form in the case where the mobility is constant. The impedance of a metal-semiconductor-metal structure is then computed, and the frequency and bias range over which a negative resistance arises is found to be consistent with known experimental data.