Overshoot mechanism in transient excitation of THz and Gunn oscillations in wide-bandgap semiconductors

A detailed study of high-field transient and direct-current (DC) transport in GaN-based Gunn diode oscillators is carried out using the commercial simulator Sentaurus Device. Applicability of drift-diffusion (DD) and hydrodynamic (HD) models to high-speed, highfrequency devices is discussed in depth, and the results of the simulations from these models are compared. It is shown, for a highly homogeneous device based on a short (2 μm) supercritically doped (1017 cm-3) GaN specimen, that the DD model is unable to correctly take into account some essential physical effects which determine the operation mode of the device. At the same time, the HD model is ideally suited to solve such problems due to its ability to incorporate non-local effects. We show that the velocity overshoot near the device contacts and space charge injection and extraction play a crucial role in defining the operation mode of highly homogeneous short diodes in both the transient regime and the voltagecontrolled oscillation regime. The transient conduction current responses are fundamentally different in the DD and HD models. The DD current simply repeats the velocity-field (v-F) characteristics, and the sample remains in a completely homogeneous state. In the HD model, the transient current pulse with a full width at half maximum of approximately 0.2 ps is increased about twofold due to the carrier injection (extraction) into (from) the active region and the velocity overshoot. The electron gas is characterized by highly inhomogeneous distributions of the carrier density, the electric field and the electron temperature. The simulation of the DC steady states of the diodes also shows very different results for the two models. The HD model shows the trapped stable anodic domain in the device, while the DD model completely retains all features of the v-F characteristics in a homogeneous gas. Simulation of the voltage-controlled oscillator shows that it operates in the accumulation layer mode generating microwave signals at 0.3 to 0.7 THz. In spite of the fact that the known criterion of a Gunn domain mode n0L > (n0L)0 was satisfied, no Gunn domains were observed. The explanation of this phenomenon is given. © 2012 Momox et al

Desarrollo y uso de la Suite GlassBox para reaprender Ciencias básicas

Se desarrolló una Suite de aplicaciones computacionales nombrada GlassBox, con el propósito de facilitarles a nuestros estudiantes el reaprendizaje de las Ciencias básicas. Con GlassBox, los estudiantes no solo centran su atención en los principios fundamentales, sino que pueden hacer observaciones cualitativas y cuantitativas de los fenómenos, trabajar de forma colaborativa para explorar los límites de los modelos mediante preguntas como “¿qué pasaría sí…?” y tener acceso completo a los componentes internos de estas cajas negras, por ejemplo: al algoritmo, a su implementación computacional y a ejercicios retadores. La Suite GlassBox se desarrolló de agosto del 2015 a julio del 2016. Ahora se adapta su uso dentro y fuera del aula para enriquecer la experiencia de aprendizaje, tanto en preparatoria como en profesional del Tecnológico de Monterrey Campus Querétaro y Ciudad de México a partir del periodo agosto-diciembre 2016.Iniciativa Novu