High magnetic field studies of donor excitation spectra in InSb

The two lowest energy spectral lines of the shallow donors in InSb involving ground to excited state transitions are studied in photoconductivity using higher spectral resolution and stronger magnetic fields than achieved previously. The observed line positions are compared with recent calculations of the high field hydrogenic donor levels and difference of the order of the effective Rydberg R¹ at zero field are found at magnetic fields where the zero point cyclotron energy exceeds R¹ by two orders of magnitude. Central-cell components of the 1s–2p transition, corresponding to four donor species are resolved, and the magnetic field dependence of the relative chemical shifts are analysed. The broader 1s–2p₀ line undergoes a coupling at an interaction energy of 37 cm^-1, the origin of which is uncertain at present.