DLTS rate window

The inverse of this time is called the DLTS rate window. In practice, of course, the boxcar gates at f, and t2 must have finite widths. In fact, for optimum signal-to-noise the gate widths should be as large as possible (Lang,... 

The conversion of temperature to an energy scale is accomplished by making an Arrhenius plot for a series of experimental DLTS rate windows (see Fig. 48 in Section 15). This will give not only the energy depth but also the prefactor, v or Vp, for each level. 

The overall energy scale is found from several spectra taken at different DLTS rate windows by making an Arrhenius plot of the high temperature peak in the voltage pulse spectra as shown in Fig. 48. The 0.94 eV slope of the raw data is corrected for the probable T dependence of the exponential prefactor by subtracting 2kT—0.06 eV to give E=0.88 eV 10%. Thus we... 

Fig. 10. DLTS spectrum for a Schottky-barrier diode on n-type ( 7 x 1015 P/cm3) silicon after hydrogenation (150°C, 50 min). The emission rate window e0 corresponds to delay times of 0.5 and 2.5 ms. Each peak is labeled with the measured activation energy for thermal emission of electrons (Johnson et al., 1987a).

SDs were fabricated on Si doped GaN ( 500 nm, 5 x 1016-2 x 1017 cm-3) using various GaN templates discussed in the previous section (see Figure 6.6) as well as one reference sample and one ELO sample. The comparison of DFTS spectra with rate window of 120 s-1 for all measured samples is shown in Figure 6.15. Since the trap concentration determined by DLTS is proportional to Np and AC i, where Np is the... 

Figure 6.15 DLTS spectra measured for all samples under study. The pulse width is 10 ms and the rate window is 120 s L Reproduced from Xie JQ et al., Applied Physics Letters 90(26) Art. No. 262112. Copyright (2007), with permission from the American Institute of Physics...

Fig. 41. Capacitance DLTS spectra for the quasi-discrete-level density of states of Fig. 16 for a 10 sec rate window. A 5 V reverse bias and an area of 2 X 10 cm were assumed in the calculation.

Proponents of this method claim that by using a fixed temperature the variation of conductivity within the sample as well as the occupation statistics are also fixed so that these spectra are more easily interpreted. Proponents of the standard DLTS method point out the enhanced ability to vary the thermal emission energy by sweeping temperature (a DLTS scan with 10 sec" rate window taken over the temperature range 100-450°Kin a-Si H is equivalent to a time scale range at 300°K of from 3 nsec to 65 hr. To the extent that the DLTS spectra for a variety of rate windows can be fit consistently to a single density of states, there should be no difference between these... 

Fig. 46. Typical DLTS hole and electron emission spectra for an a-Si H sample doped with 300 ppm PH3. (10 sec" rate window, 5 V reverse bias on rear junction.)...

Fig. 48. DLTS measurement time constant t (inverse of rate window) versus the inverse temperature of the peak in the electron emission spectrum at that r for a typical sample. The activation energy of 0.94 eV is the slope of the raw data without the 2kT correction (see text). The circles are from DLTS spectra the triangles are calculated from directly recorded capacitance transients.

Fig. 60. Set of five DLTS electron emission spectra corresponding to different amplitudes of the 10 msec bias voltage pulse used to fill the gap states with electrons. The arrows indicate the DLTS peak positions calculated for pulse amplitudes less than S V using a spatially uniform g(E) fit to the 5 V pulse data. (10 sec rate window, 5 V reverse bias on rear junction, sample JH139.) [From Lang et al. (1982a).]...

The activation energy derived for the data displayed in Fig. 48 needs no further comment. However, let us consider some adffitional evidence. In Fig. 62 the DLTS spectra for one sample using two different rate windows are shown (Lang et al, 1982a). The exponential prefactor is precisely the quantity that determines how the DLTS should change with rate window. The solid lines through the solid data points are spectra calculated from the density of states derived from the 100 msec rate window data. The solid lines... 

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