A suitable simple optical cryostat for optical, magneto-optical, electrical and thermo-electrical measurements was designed. It is suitable for use in a magnetic pool gap as narrow as less than 1 cm. Throughout a long period of time, the heat diffusion process of the cryostat can be easily operated at slow increase in sample temperature in a range 1.25 K/min at 200 K that will be reduced gradually to 0.66 K at room temperature. Liquid nitrogen was used to cool down the temperature. During the operation, the change in the measured energy gap of a semiconductor sample and other physical parameters resulting from the change of temperature can be corrected through the temperature coefficient of that parameter at the corresponding temperature. The cryostat was successfully used for all experiments mentioned above to measure the properties of a single crystal of GaP (Gallium Phosphate) semiconductor.
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