We transform the n-dimensional ambipolar transport equation to the n-dimensional nonhomogeneous heat equation, which has been solved for most common initial and boundary conditions. Thus, general solutions to the nonhomogeneous heat equation, obtained in a robust form through finite Fourier transforms, provide an easy approach to solving the ambipolar transport equation, which previously had been solved with more difficulty through Laplace transform techniques. We then obtain a general analytic one-dimensional time-dependent solution to the excess carrier and current densities in a pn junction diode in response to a transient radiation or light pulse under low-injection conditions. We derive most of the known analytic solutions to this problem and we examine the limiting behavior of these solutions to show that they are consistent. The model includes the effects of a constant electric field in the quasineutral region, a finite diode length, and an arbitrary generation function in terms of space and time. In the area of light communication, we use the model to examine the impact of doping parameters on the buildup of diffusive photocurrent that limits the signal bandwidth. Solutions to the ambipolar diffusion equation assuming more general initial and boundary conditions are easily obtained via the given transformation. The model may be applied to problems involving photodiodes, light-emitting diode or laser communication, transient radiation effects in microelectronics, dosimetry, or the response of solar cells to light.

The structural, surface morphology, and the temperature dependence photoluminescence of InGaN(3 nm)/GaN(7 nm) 5 period multi-quantum-well blue-light-emitting diode (LED) structures grown by metal organic chemical vapor deposition (MOCVD) have been studied. Quantum dot-like structures and strain contrast evident by black lumps were observed in the quantum wells using high-resolution transmission electron microscopy (HRTEM) analysis. Double-crystal high-resolution x-ray diffraction (HRXRD) spectra of blue LED were simulated using kinematical theory method, to obtain composition, and period thickness of well and barrier. The “S” shape character shift as red–blue–redshift of the quantum-well emission line, i.e., blue emission peak 2.667 eV at 10 K, was observed with variation of temperature in the photoluminescence (PL) spectra. The shift is assigned to the potential fluctuations due to alloy inhomogeneous distribution in the quantum wells. The In composition in the quantum wells obtained by two independent techniques, namely HRXRD and PL, was 8% and 19%, respectively. The reason for this large difference in composition is explained in this letter.

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Circuit simulation tools (e.g., SPICE [1]) have become invaluable in the development and design of electronic circuits in radiation environments. These codes are often employed to study the effect of many thousands of devices under transient current conditions. Device-scale simulation tools (e.g., MEDICI [2]) are commonly used in the design of individual semiconductor components, but require computing resources that make their incorporation into a circuit code impossible for large-scale circuits. Analytic solutions to the ambipolar diffusion equation, an approximation to the carrier transport equations, may be used to characterize the transient currents at nodes within a circuit simulator. We present new transient 1D excess carrier density and photocurrent density solutions to the ambipolar diffusion equation for low-level radiation pulses that take into account a finite device geometry, ohmic fields outside the depleted region, and an arbitrary change in the carrier lifetime due to neutron irradiation or other effects. The solutions are specifically evaluated for the case of an abrupt change in the carrier lifetime during or after, a step, square, or piecewise linear radiation pulse. Noting slow convergence of the raw Fourier series for certain parameter sets, we use closed-form formulas for some of the infinite sums to produce "partial closed-form" solutions for the above three cases. These "partial closed-form" solutions converge with only a few tens of terms, which enables efficient large-scale circuit simulations.

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