Function Of Surface Recombination Velocity Research Articles

Numerical simulations of two-photon absorption time-resolved photoluminescence to extract the bulk lifetime of semiconductors under varying surface recombination velocities

We investigate the limitations of two-photon absorption time-resolved photoluminescence to measure the low-injection bulk lifetime of different semiconductor materials under varying surface recombination. The excitation source is assumed to be a sub-bandgap pulsed laser and the localized absorption and carrier generation was modeled using a focused TEM00 Gaussian beam under the assumption of diffraction-limited performance. The subsequent carrier kinetics were simulated by applying the finite-difference time-domain method to the continuity equation. Three typical semiconductor materials were modeled: direct bandgap low-mobility material (such as CZTS), direct bandgap high mobility (such as GaAs), and indirect bandgap high mobility (such as float-zone silicon). The extracted effective lifetime as a function of surface recombination velocity was compared to the bulk lifetime and the effective lifetime calculated using an analytical 1D approximation. For the direct bandgap materials, focusing inside the material yields an effective lifetime within a few percent of the bulk lifetime, regardless of the surface recombination velocity, while for excitation close to the surface it is up to 30% lower than the bulk lifetime at high surface recombination velocities (>104 cm/s). For the indirect bandgap material, the effective lifetime is dominated by the surface, making the bulk lifetime inaccessible, even at surface recombination velocities of 100 cm/s. Finally, we use the 1D approximation to find under what conditions the bulk lifetime can be extracted by this method and determine that both the bulk diffusion length and the product of the bulk lifetime and surface recombination velocity must be much less than twice the device thickness.

Modeling the DC gain of 4H–SiC bipolar transistors as a function of surface recombination velocity

Two dimensional device modeling is used to investigate the differential DC current gain in 4H–SiC bipolar junction transistors using surface recombination velocity as one of the physical variables affecting the current gain. The simulated differential gain is compared with the measured experimental DC gain of transistors with two different emitter lengths. The comparison and the analysis made support the trend in modeling the DC gain as a function of surface recombination velocity and show that higher gain can be obtained for transistors with lower surface recombination velocity.

Self-consistent calculation of facet heating in asymmetrically coated edge emitting diode lasers

A numerical model is introduced that self-consistently calculates the time dependent axial variations of photon density, carrier density and temperature in semiconductor lasers. The most important approximations are outlined. In order to illustrate the capability of the model, some results are shown for an asymmetrically coated DQW GaAs/GaAlAs edge emitting laser diode. The temperature rise at the facets and the corresponding profiles of carrier and photon density are calculated. The asymmetric behaviour of the profiles is discussed. The heating is calculated as a function of surface recombination velocity at the mirrors and as a function of injection current. The calculations provide insight into the process of facet heating and catastrophic optical damage. The calculations are confirmed by experimental investigations.

The effect of surface recombination on surface photovoltage in semiconductors

A numerical method is used to evaluate the surface photovoltage (SPV) in semiconductors as a function of surface recombination velocity, photon flux, substrate doping level, and oxide charge. It is found that SPV is reduced by the surface recombination. For a certain surface recombination velocity SPV increases approximately as the logarithm of photon flux. The effect of surface recombination on SPV is dependent on substrate doping level and oxide charge, to sum up, on the energy-band bend. SPV for depletion surface is more remarkably affected by surface recombination than that for strong inversion surface.

Bulk and surface components of recombination lifetime based on a two-laser microwave reflection technique

An algorithm for separating the bulk and surface components of recombination lifetime, tailored for contactless measurement techniques with laser excitation, is presented in the paper. In order to analyze the carrier decays and subtract the surface recombination term, two lasers operating at 910 and 830 nm are applied. A separation of carrier decay resulting from the different contribution of surface and bulk components due to difference in the light absorption is observed for such a case. This separation is a function of surface recombination velocity S. An experimental verification of the analysis is presented using microwave absorption/reflection measurements.

An analysis of the photoinduced current from a finely focused light beam in planar p-n junctions and Schottky-barrier diodes

We present analytic expressions for the photocurrent generated by a highly convergent light beam from a microscope objective lens incident on both planar p-n junctions and Schottky-barrier diodes. The variation of the current as a function of surface recombination velocity, depletion region width, diffusion length, and objective lens numerical aperture are all discussed. We also consider the application of the technique as a method of measuring minority-carrier diffusion lengths, which is independent of variations in surface reflectivity.

Dember effect in fast photoconductive circuit elements

The observed independence of mobility on surface conditions in InP:Fe fast photoconductivity devices is explained by inclusion of the Dember electric field resulting from unequal electron and hole mobilities. From the calculated electron-concentration distribution as a function of the distance normal to the device surface, we determine that the mean position of the electron concentration in InP lies more than one standard deviation below the surface for laser excitation of 780 nm and a high-injection ambipolar surface recombination velocity of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> cm/s. Results are presented for InP:Fe as a function of surface recombination velocity, and related results are presented for Si and for a material with equal hole and electron mobilities.

Theory, design, and performance of low-blooming silicon diode array imaging targets

The increase in size of an image produced by a high intensity source is particularly troublesome in silicon diode array imaging devices. This increase is caused by inversion of Si under the SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> between the diodes or by the lateral diffusion of the excess minority carriers in the field-free region of the sensor array. The formation of inversion layers can be eliminated by proper choice of the sheet resistance of the resistive sea when the target is operated above flat-band voltage. However, when the diodes in the image are fully discharged in a time interval shorter than the frametime, the excess carriers diffuse to the adjacent diodes and cause an increase in the size of the image. Such "blooming" is related to the effective minority carrier lifetime that is a function of surface recombination velocity at the imaging side of the target, surface recombination velocity at the diode side of the target, and bulk minority carrier lifetime. Two methods for controlling blooming will be discussed. In one case, the effective minority carrier lifetime is reduced by adjusting the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> doping profile at the imaging side of the array. The second technique requires diffusion of a separate p-type region, placed between the sensing diodes elements, which provides a high recombination region when the sensing diodes are discharged due to the image overload. Devices have been constructed with good imaging quality, where a 1 percent scan diagonal bright spot bloomed to 4 percent in the first technique, and to 2.5 percent in the second technique with a 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> overload above saturation. The data are in good agreement with the theory.

Effects of surface recombination and geometry in alloy junction transistors

Collector to base current amplification factor (α cb ) in alloy junction transistors has been studied as a function of surface recombination velocity (S) for the case where emitter is bigger than the collector. Calculations have been done for transistors with collector diameter varying from 0·005 cm to 0·07 cm and emitter to collector radius ratio ( b/ a) from 2 to 10. The ratio of normal and inverse amplification factors (α N /α I ) has been calculated as a function of ‘ S’ and has been compared with the experimental observations of Moore and Pankove [2].