Resonant donor-bound-exciton luminescence in semiconductors

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Abstract
The authors report novel ultra-sharp satellite luminescence lines when excited states of neutral-donor bound excitons (BE) are resonantly excited in ZnTe by a narrow laser line. The spectral position and magnetic characteristics indicate 'two-electron' transitions, leaving the donor in a series of ns and np excited orbital states. Optical pumping of the inhomogeneously broadened lines in the best crystal provides an almost tenfold linewidth reduction compared with normal BE transitions, toward a value comparable with both the laser line and the homogeneous lifetime broadening of the BE. This narrowing is greatly advantageous in the difficult task of distinction between donor species in medium to narrow direct-gap semiconductors. Orbital and spin magnetic splittings provide accurate values for electron effective mass and g value. The intensity ratio of transitions to s and p orbital states yield information on the character of the BE excited states, in agreement with recently published data of Romestain and Magnea (1979).