Spectroscopic measurement
of Energy Gap in semiconductors

The apparatus allows a spectroscopic measurement of the energy gap in semiconductors (Ge, Si) at room temperature.

The internal photoelectric effect (photon absorption and electron-hole pair production) is excited by monochromatic light, whose wavelength is continuously changed by rotating a reflection diffraction grating and modulated by a chopper.

Both the signal due to absorbed photons  (photoconductivity) and  the signal produced by photons
transmitted through the thin semiconductor sample are counted simultaneously by a  two-channel lock-in  amplifier driven by the chopper reference signal.

The grating rotation is driven by a motor and the working wavelength is calculated from the rotation angle measured by a built-in encoder.

The absorption  spectrum is obtained from the sample resistance  changes, and the transmission spectrum from the light measured by a pyroelectric detector.

A measurement without sample provides the emission spectrum of the light source (incandescent lamp).

A PC  is  used as controller, data-storage and data-handling system, through an interface (3.channel data logger connected via USB).

see also:
Sconza A., Torzo G. :Spectroscopic measurement of the semiconductor energy gap , Am. J. Phys 62, 732-737(1994)

Eg setup