Hot Carrier Mobility Research Articles

Enhanced Carrier Lifetime and Mobility in Monolayer NbOI2.

The lifetime and mobility of hot carriers are critical parameters for assessing the performance of optoelectronic materials, as they directly impact the response speed and operational efficiency of devices. Combining first-principles calculations with nonadiabatic molecular dynamics (NAMD) simulations, we systematically investigated the electronic properties and carrier dynamics of monolayer NbOI2. Our findings indicate that, at room temperature, this material demonstrates a carrier lifetime of up to ∼13 ns and an electron mobility reaching as high as ∼9 × 103 cm2 V-1 s-1. The low Young's modulus makes it susceptible to deformation under external stress, and we found that the carrier lifetime extends to ∼40 ns under a 4% tensile strain, along with a significant increase in hole mobility. This study elucidates the carrier dynamics in monolayer NbOI2, facilitating its potential application in future flexible optoelectronic devices.

Multipulse Terahertz Spectroscopy Unveils Hot Polaron Photoconductivity Dynamics in Metal-Halide Perovskites.

Hot carriers in metal-halide perovskites (MHPs) present a foundation for understanding carrier-phonon coupling in the materials as well as the prospective development of high-performance hot carrier photovoltaics. While the carrier population dynamics during cooling have been scrutinized, the evolution of the hot carrier properties, namely mobility, remains largely unexplored. Here we introduce novel ultrafast visible pump-infrared push-terahertz probe spectroscopy to monitor the real-time conductivity dynamics of cooling carriers in methylammonium lead iodide. We find a decrease in mobility upon optically re-exciting the carriers, as expected for band transport. Surprisingly, the conductivity recovery is incommensurate with the hot carrier population dynamics measured by infrared probe and exhibits a negligible dependence on the hot carrier density. Our results reveal the importance of localized lattice heating toward the hot carrier mobility. This collective polaron-lattice phenomenon may contribute to the unusual photophysics of MHPs and should be accounted for in hot carrier devices.

Hot carrier transport in modulation doped Si/SiGe and Ge/SiGe heterostructures

In this paper we report studies carried out on 2D electrons in strained silicon and 2D holes in strained germanium channel modulation doped heterostructures, to understand their high field transport properties. Geometric magnetoresistance technique was used to measure the mobility as a function of the applied field up to 300 V/cm and for lattice temperatures from 10 to 160 K. We observe that at high fields the mobility decreases at a faster rate in the germanium channels compared with silicon channels. Empirical relations were fitted to the data. Theoretical calculations using Boltzmann transport theory and Green's function for non-linear transport at high fields are also presented. We find that the Green's function approach is better suited to explain the hot carrier mobility degradation in these high mobility samples.

Breakdown electroluminescence spectra in structures based on the solid solutions Ga1?xAxP(As)

The authors investigate the breakdown luminescence spectra in reverse-biased p-n heterojunctions based on gallium and aluminum phosphides and arsenides for the purpose of determining their behavior as lasing and photodetection materials. Data are given on temperature coefficients, band gap structure, bremsstrahlung, hot carrier mobility and photon emission, and transition and recombination parameters.

Experimental Determination of the Energy Distribution Functions and Analysis of the Energy-Loss Mechanisms of Hot Carriers inp-Type Germanium

This paper contains a description of an experimental determination of the energy distribution functions of hot holes in germanium, and the application of the results to the analysis of the dominant scattering and energy-loss mechanisms. The distribution functions are obtained from the study of the modulation of the free-hole, intervalence-band absorption of infrared radiation by application of pulses of high electric field. Details of the distribution function can be obtained because a correlation exists between the absorption at a given wavelength and the hole concentration at a given energy. An auxiliary investigation of the temperature dependence of the equilibrium absorption spectrum empirically supplies the necessary calibrating relations for the above correlation and an approximate valence-band structure with equivalent spherical energy surfaces. The hot-carrier studies were made at field strengths up to 2800 V/cm, at 77\ifmmode^\circ\else\textdegree\fi{}K, on germanium samples with hole concentrations in the range of ${10}^{15}$/${\mathrm{cm}}^{3}$. The infrared modulation effects are themselves of interest and the techniques are described in detail. Positive and negative modulation of transmitted intensity as high as 50% could be obtained. The dependence of the modulation (and distribution functions) on crystallographic direction, carrier concentration, and polarization of the light was investigated. Three features of the experimental distributions stand out: (a) the non-Maxwellian character, typified by the relatively small number of high-energy carriers, (b) the slow rise in average energy from 0.01 to 0.028 eV as the field strength is raised to 2000 V/cm, and (c) the large ratios of drift to root-mean-square velocity, $\frac{{v}_{\mathrm{d}}}{{v}_{\mathrm{rms}}}\ensuremath{\gtrsim}0.4$ for Eg400 V/cm, corresponding to strong displacement of the hole distributions in momentum space. These features, together with energy-loss rate calculations, substantiate the importance of inelastic scattering and the dominant role of optical-phonon interactions. A picture of the steady-state hot-carrier effect emerges, emphasizing a cyclic streaming motion of holes in k space, in contrast to the usual diffusion formulation. Briefly indicated are some consequences of this picture regarding the relative population of light and heavy holes, the anisotropy of infrared absorption and hot-carrier mobility, and the efficiency of impact ionization of deeplying acceptors.

Scattering of hot carriers in germanium

The variation of lattice mobility of hot carriers with their average energy or “temperature” has been investigated. An expression is derived for the relaxation time due to single phonon acoustical mode scattering which remains valid to very high carrier temperatures at lattice temperatures of 20°K and above. In the limit where carriers interact mainly with lattice oscillators having only zero point energy it is found that the relaxation time is proportional to the inverse square of the speed rather than to the inverse first power as for thermal carriers. Lattice mobility is plotted as a function of average carrier energy for various values of the ratio of coupling constants for optical and acoustical modes, and various effective masses, for lattice temperatures of 300°, 78° and 20°K. The effect of dropping the assumption of equipartition of energy among the acoustical lattice oscillators is to increase the scattering effect of the acoustical modes, the more so the lower the lattice temperature, the higher the carrier temperature, and the higher the mass of the carriers. Impurity scattering has not been included in the quantitative calculations, but it is shown that the increase in hot-carrier mobility which can be caused by this scattering process will generally be less than has been expected.

Lattice mobility of hot carriers

Lattice mobility of hot carriers