Excited-state laser spectroscopy of the impurities in III–V and II–VI semiconductors

At temperatures where the shallow donors become occupied, weak impurity lines appear on sweeping the field with laser wavelenghts where photon energy is insufficient to cause transitions from the ground state ti any of the excited states if the impurities. With all the materials investigated, the two most prominent of these lines, which are attributed to transitions between excited states, lie on the same two curves on a dimensionless diagram of excitation energy against cyclotron energy. One of these lines is identified as arising from the 2p⁻ to 2s transition. The other probably also originates from the 2p⁻ state. The photon energy for the 311μ laser line is just sufficient to cause transitions from the 1s to 2p⁻ state in n-GaAs. Because of this almost exact coincidence, fine structure due to the central cell corrections for individual impurities is particularly well resolved in magnetic field.