Low-cost apparatus for determining the band gap energy in photoresistors

The energy band gap is crucial for operating various optoelectronic devices such as LEDs, diodes, transistors, and photovoltaic cells. In this work, we developed a low-cost setup to determine the band gap of the semiconductor material used in light-dependent resistors (LDRs). The apparatus uses a diffraction grating to produce light of different wavelengths that shines on the LDR. The curve of the electrical resistance versus the incident light energy is used to determine the band gap, defined as the energy of the first inflection point of the curve. We obtained a band gap that differed by 5% from the expected value for the ternary semiconductor alloy assumed to be used in the LDR. The proposed setup can be used in higher education experimental physics courses to address solid-state physics topics, and also in high school to introduce modern physics concepts.

Keywords:
Band gap; Semiconductor; Light-dependent resistor (LDR); Diffraction grating; Solid state physics