In 1974, when Lang devised the DLTS method, there was no advanced computer technology as there is today.The principle of DLTS spectrum measurement in the method of Lang et al. is shown in Figure A-4. Without completely collecting the transient waveform, measure the capacitance values C(t1) and C(t2) at two times t1 and t2 by an analog method (Boxcar method), and determine the difference S(T)=△C(t1)- C(t2).
When such measurement is continuously performed while changing the temperature from low to high, the capacitance transient appears prominent when reaching the temperature at which the thermal activation of the carrier trapped in the deep level began, as shown in Figure A-4 (a). Therefore, a spectrum (DLTS spectrum) where S(T) becomes maximum at this temperature (Tmax) is obtained.
The capacitance transient has an exponential change as shown in formula (A-1), but the following relationship is obtained between the time constant: τe and the above t1 and t2.
Therefore, the DLTS spectrum in Figure A-4 shows that the temperature at which the thermal emission time constant of electrons from the target deep level becomes τe is the peak point temperature: （Tmax）.