Trap recharging wave mode with a linear dispersion law for space-charge waves in $\mathrm{CdTe}:\mathrm{Ge}$

ac and dc currents arising in $\mathrm{CdTe}:\mathrm{Ge}$ during optical excitation of space-charge waves (SCW) have been investigated. The experiments have been performed at a wavelength of $\lambda =1064\mathrm{nm}$ using the technique of an oscillating interference pattern. Our investigations have shown that the SCWs studied can be attributed unambiguously to trap recharging waves (TRWs). Remarkably, we have found a linear dispersion law $({\Omega }_K\propto K)$ for these waves although an inverse law is usually expected. A corresponding theoretical model has been developed and shows that the theoretical data are in reasonable agreement with the experiments if the following fitting parameters are used: An effective trap concentration of $N_{\mathrm{eff}}=(2.5\pm 0.3)\times {10}^{12}{\mathrm{cm}}^{-3}$, a mobility-lifetime product of $\mu \tau =(0.65\pm 0.05)\times {10}^{-7}{\mathrm{cm}}^2∕\mathrm{V}$, and a Maxwell relaxation time of ${\tau }_M=(5.5\pm 0.2)\times {10}^{-3}\mathrm{s}$. The appearance of an additional low-frequency ac resonance is discussed in the frame of a bipolar conductivity.

Figure 1

(a) Experimental setup (schematically). LP, combination of a half-wave plate and a polarizer; BS, beam splitter; BP, beam splitting plate; PM, phase modulator; BE, beam expander; M, mirror; PRC, the studied crystal. A $\mathrm{YAG}:\mathrm{Nd}$ laser at $\lambda =1064\mathrm{nm}$ was used. (b) Diagram demonstrating the electronic detection of SCW. HV, high-voltage source; RL, loading resistor; FG, function generator; VM, voltmeter for dc measurements.

Figure 2

Frequency dependence of the output ac signal for $W_0=100\mathrm{mW}∕{\mathrm{cm}}^2$, $E_0=1.5\mathrm{kV}∕\mathrm{cm}$, $K=0.1\times {10}^4{\mathrm{cm}}^{-1}$, $m=0.6$, and $\Theta =0.3\pi$.

Figure 3

(a) Frequency dependence of the ac output signal. (b) Frequency dependence of the dc output signal for $W_0=100\mathrm{mW}∕{\mathrm{cm}}^2$, $E_0=2.0\mathrm{kV}∕\mathrm{cm}$, $K=0.31\times {10}^4{\mathrm{cm}}^{-1}$, $m=0.6$, and $\Theta =0.3\pi$. The lines are calculations in accordance with Eqs. (5, 6, 7).

Figure 4

Position of the resonance peak for the high- and low-frequency resonance as a function of the wave number $K$ for $W_0=100\mathrm{mW}∕{\mathrm{cm}}^2$, $E_0=1.5\mathrm{kV}∕\mathrm{cm}$, $m=0.6$, and $\Theta =0.3\pi$. The line is a calculation in accordance with Eq. (4).

Figure 5

Position of the resonance peak for the high-frequency resonance as a function of the applied electric field $E_0$ for $W_0=100\mathrm{mW}∕{\mathrm{cm}}^2$, $m=0.6$, $\Theta =0.3\pi$, and $K=0.32\times {10}^4{\mathrm{cm}}^{-1}$. The line is a calculation in accordance with Eq. (4).

Figure 6

Position of the resonance peak for the high-frequency resonance as a function of average light intensity for $E_0=3.0\mathrm{kV}∕\mathrm{cm}$, $m=0.6$, and $\Theta =0.1\pi$, and two different values of $K$.