The diffusion process of metastable carriers in bismuth

Abstract

The diffusion process of electrons and holes which have been pumped into a metastable band in bismuth films by a 1.064-fim laser pulse is considered in the calculation of the induced thermal gradient. The fit between the temporal evolution of this calculated thermal gradient and that of the thermoelectric response of films to the laser excitation allows us to estimate an upper limit of the ambipolar diffusion coefficient of metastable carriers.

Classical size behavior of the Nernst-Ettingshausen effect induced by pulsed laser light in bismuth films

“…5 This observation, together with that of Ref. 1, reveals the important influence of the surface on the laser-induced transport phenomena.…”

“…The detailed calculation of the temporal evolution of ٌT p can be found elsewhere. 5,7,8 Table I gives the estimated values of ٌT p and the corresponding irradiation energy density r for each film. The measured behavior of the coefficient Q NE with the magnetic field is shown in Fig.…”

“…We have previously reported that a surface effect appears in bismuth films when a thermal gradient is generated by irradiation with short laser pulses, the effect being due to the inhomogeneous heating of the films and the presence of a surface near the region where the thermal gradient is higher. 5 We can roughly divide the film into two parts: a superficial slice of thickness d s where the temperature gradient appears and an inner slice of thickness dϪd s where it is considered that the temperature is not altered by irradiation. The thickness d s , taken as the depth at which the induced temperature increases, is a certain fraction, in our case 1/e, of the superficial temperature increase.…”