Drift velocity and diffusion coefficients from time-of-flight measurements

Canali, C.; Nava, F.; Reggiani, L.

doi:10.1007/3-540-13321-6_3

Cited by 14 publications

(5 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This value fits well with reported values for the majority carrier diffusivity reported in literature for degenerately doped, p-type silicon89 .…”

supporting

confidence: 92%

Quantifying nanoscale carrier diffusion with ultrafast optical and photocurrent microscopy

Block

View full text Add to dashboard Cite

Heat transport in solids is one of the oldest problems in physics, dating back to the earliest formulations of thermodynamics. The classical laws of heat conduction are valid as long as the observed time and length scales are larger than the relaxation time and mean free path of the underlying microscopic heat carriers, such as electrons and phonons. With the advent of ultrafast lasers and nanoscale systems these regimes can now be surpassed and new refined models of heat transport are needed. In particular, the interaction of ultrashort light pulses with matter can excite electrons to high temperatures, leading to a local non-equilibrium of electrons and phonons. Under these conditions, also the transport properties of the carriers are altered. So far, these effects have typically been studied in the time domain. The cooling of photo-excited hot electrons has been studied both in metals as well as novel 2D materials, such as graphene. However, due to a lack of spatio-temporal resolution, it has not been possible to distinguish the effects of hot-electron diffusion from other cooling mechanisms, such as electron-phonon coupling. In this thesis, I directly track such ultrafast heat and carrier diffusion in space and time with ultrafast microscopy. By using the recently developed technique of probe-beam-scanning transient-absorption microscopy on thin gold films I directly resolve, for the first time, a transition from hot-electron diffusion to phonon-limited diffusion on the picosecond timescale. I support the understanding of these complex dynamics by theoretical modeling of the thermo-optical response based on a two-temperature model. I apply the same technique to study hot carrier diffusion in atomically thin monolayer graphene. By comparing differently prepared samples, I study the strong influence of external parameters, such as production type, substrate, and environment on carrier diffusion. Finally, I study hot carrier diffusion in exfoliated and encapsulated graphene devices with a novel technique of ultrafast spatio-temporal photocurrent microscopy based on the photothermoelectric effect. I extract diffusion dynamics for electrically characterized samples with the help of theoretical spatio-temporal modeling, thereby testing the fundamental relationship between electrical and thermal carrier transport. The precise quantification of ultrafast and nanoscale carrier transport with these state-of-the-art techniques leads to a broader understanding of non-equilibrium dynamics and could ultimately help the design, optimization, and heat management of the next generation of ultra-compact (opto-) electronic devices, such as solar cells, photodetectors, or integrated circuits. El transporte de calor en sólidos es uno de los problemas más antiguos de la física, que se remonta a las primeras formulaciones de la termodinámica. Las leyes clásicas de la conducción de calor son válidas cuando las escalas de tiempo y longitud observadas sean mayores que el tiempo de relajación y la trayectoria libre media de los portadores de calor microscópicos subyacentes, como los electrones y los fonones. Con la llegada de los láseres ultrarrápidos y los sistemas a nanoescala, estos regímenes ahora pueden superarse por lo cual se necesitan nuevos modelos refinados de transporte de calor. En particular, la interacción de pulsos de luz ultracortos con la materia puede excitar electrones a altas temperaturas, lo que lleva a un desequilibrio local de electrones y fonones. En estas condiciones, también se modifican las propiedades de transporte de los portadores de calor. Hasta ahora, estos efectos han sido típicamente estudiados en el dominio del tiempo. El enfriamiento de electrones calientes fotoexcitados se ha estudiado tanto en metales como en nuevos materiales bidimensionales, como el grafeno. Sin embargo, debido a la falta de resolución espacio-temporal, no ha sido posible distinguir los efectos de la difusión de electrones calientes de otros mecanismos de enfriamiento, como el acoplamiento de electrones y fonones. En esta tesis, hago un seguimiento directo de la difusión del calor y sus portadores en el espacio y el tiempo con microscopía ultrarrápida. Al utilizar la técnica recientemente desarrollada de microscopía de absorción transitoria con escaneo de sonda en películas de oro delgadas, resuelvo directamente, por primera vez, una transición de la difusión de electrones calientes a la difusión limitada por fonones en la escala de tiempo de picosegundos. Apoyo la comprensión de estas dinámicas complejas mediante el modelado teórico de la respuesta termo-óptica basada en un modelo de dos temperaturas. Aplico la misma técnica para estudiar la difusión de portadores calientes en una capa de grafeno atómicamente delgado. Al comparar muestras preparadas de manera diferente, estudio la fuerte influencia de los parámetros externos, como el tipo de producción, el sustrato y el entorno sobre la difusión del portador. Finalmente, estudio la difusión de portadores en dispositivos de grafeno exfoliados y encapsulados con una técnica novedosa de microscopía de fotocorriente espacio-temporal ultrarrápida basada en el efecto fototermoeléctrico. Extraigo dinámicas de difusión para muestras caracterizadas eléctricamente con la ayuda del modelado espacio-temporal teórico, probando así la relación fundamental entre el transporte eléctrico y térmico. La cuantificación precisa del transporte de los portadores ultrarrápido y a nanoescala con estas técnicas de vanguardia lleva a una comprensión más amplia de la dinámica del no equilibrio y podría, en última instancia, ayudar al diseño, la optimización y la gestión del calor de la próxima generación de dispositivos (opto-)electrónicos ultracompactos, como células solares, fotodetectores o circuitos integrados.

show abstract

“…This value fits well with reported values for the majority carrier diffusivity reported in literature for degenerately doped, p-type silicon89 .…”

supporting

confidence: 92%

Quantifying nanoscale carrier diffusion with ultrafast optical and photocurrent microscopy

Block

View full text Add to dashboard Cite

show abstract

“…Even if there is uniqueness, the reconstruction must be extremely unstable as we have seen from this paper that the reconstruction of one unknown N ðxÞ is already very ill-posed. We acknowledge, however, that the diffusivity and mobility parameters can indeed be fitted from experimental data under much simplified setting; see for example the discussion in [10,51,56]. To deal with the ill-posedness of the inverse problem, we parameterized the doping profile to reduce the number of unknowns to be reconstructed.…”

Section: Conclusion and Remarksmentioning

confidence: 99%

“…The aim of parameter extraction is to recover material parameters of devices from measurement of device characteristics, such as the voltage-to-current (I-V) data and the voltage-to-capacitance (C-V) data. The parameters that are of interests are mainly the doping profile [19,24,34,47] and the carrier mobilities [10,51,56], but there are also significant interests in other material parameters such as thermal and electrical conductivities [30,31].…”

Section: Introductionmentioning

confidence: 99%

Recovering doping profiles in semiconductor devices with the Boltzmann–Poisson model

Cheng

Gamba

Ren

2011

Journal of Computational Physics

View full text Add to dashboard Cite

“…In many cases, however, the experiment can be designed in such a way that only one major process is controlling the time-dependence of the observed LET signal arising at the resistor in the external circuit. A prominent example of such a case is the determination of the drift mobility of charge carriers from the transit time through trap free material in the so called "time of flight" experiment at a photoconductor (semiconductor or insulator) of known dimensions [11,12]. Another example is the analysis of the rise time of the transient which is controlled by the slowest step of light induced charge carrier injection into the photoconductor [6].…”

Section: Introductionmentioning

confidence: 99%

Laser Induced Electrical Transients at Semiconductor Electrodes

Willig

1988

Ber Bunsenges Phys Chem

View full text Add to dashboard Cite

Electrical Properties / Interfaces / Photoelectrochemistry / Semiconductors / Transients Laser-induced electrical transients (LET) are described in a model with two capacitors in series, two current source terms, a measuring resistor, and a resistor for the system. Calculated and experimental LET signals at semiconductor electrodes are shown for characteristic kinetic situations in three different time windows t < T, t comparable to T, and t > T, where T represents the RC response time of the circuit.

show abstract

Drift velocity and diffusion coefficients from time-of-flight measurements

Cited by 14 publications

References 41 publications

Quantifying nanoscale carrier diffusion with ultrafast optical and photocurrent microscopy

Quantifying nanoscale carrier diffusion with ultrafast optical and photocurrent microscopy

Recovering doping profiles in semiconductor devices with the Boltzmann–Poisson model

Laser Induced Electrical Transients at Semiconductor Electrodes

Contact Info

Product

Resources

About