radiometry system interfaced the monochromator and detectors with the acquisition

software. This unit also functioned as chopper controller and lock-in amplifier as well. A

thermo-electric cooled, Ge photodiode on the second exit port of the monochromator

detected the near IR spectrum.

3.3.2 Q-V Measurement

 The set-up for electrical measurement is shown in Fig. 3.5. A Tektronix TDS 510A

digitizing oscilloscope is used to measure the voltage at three points which are indicated

as V1, V2, V3 respectively. The voltage drop across the device was calculated as V2-V1,

and the voltage drop across the resistor was calculated as V1-V3. The current passing

through the device was calculated by dividing the voltage drop across the resistor by its

resistance, i.e.,


 13
 R

 The external charge was calculated by integrating the current over time, i.e.,


 Q = idt
 Q=\idt


 The data were collected on the Tektronix 510A oscilloscope from a Si-diode

photomultiplier tube (PMT) manufactured by Oriel with IkQ bridge resistor.