Photo-thermal ionization spectroscopy

Impurity photoconductivity (extrinsic photoconductivity) is a type of absorption measurement where the detector is the sample itself. Classical photoconductivity occurs when the absorption of an electron or of a hole takes place between a discrete state and a continuum, where it can contribute to the electrical conductivity. When the final state of a discrete transition is separated from the continuum by an energy comparable to k T at the measurement temperature, the electron or the hole in this state can be thermally ionized in the continuum and give rise to photoconductivity at the energy of the discrete transition. This two-step process, which is temperature-dependent, is known as photo-thermal ionization spectroscopy (PTIS) and is discussed in more detail later in the section on extrinsic photoconductors. 

H. Buijs, (1985) Photo thermal ionization spectroscopy for shallow donor impurity determination in GaAs. BOMEM application note no. 1... 

---