The greater the width of the band gap, the more suitable a semiconductor material is for operation at room temperature. Reducing a detector’s physical size also improves its performance at room temperature because the detector will contain fewer electrons. Fewer electrons means less thermionic noise.

To reduce the thermionic noise(where electron in the semiconductor might have sufficient thermal energy to climb to the conduction band) which deteriorates the detector resolution.

Intrinsic layer has the property that, in thermal equilibrium, the number of conduction band electrons per unit volume, is equal to the number of valence band holes. The intrinsic region presents a larger volume in which photons can produce electron hole pairs, increased quantum efficiency.

are insulators. The band gap is greater than 5 eV making the light emitted of too high energy (shorter wavelength). To reduce the energy, an activator impurity is added to the crystal.

Parallel plate electrodes

Co-axial electrodes