Bandgap Modulation in ZnO by Size, Pressure, and Temperature

The effect of crystal size, pressure, temperature, and their coupling on the bandgap (E-G) of ZnO crystals have been investigated based on the Hamiltonian perturbation, using the extended BOLS correlation theory The functional dependence of the E-G on the identities (order, nature, length, energy) of the representative bond for a specimen and the response of the bonding identities to the applied stimuli have been established Theoretical reproduction of the measurements confirms that the E-G expansion originates from the bond contraction/compression and bond strength gain due to (i) Goldschmidt-Pauling's rule of bond contraction induced by undercoordination, (ii) low-temperature enhanced stability, and (iii) mechanical energy storage It is found that the multiple-field coupling effect dominates in the surface skin up to three atomic layers. The presented approach provides a guideline for harnessing the photoluminescence, photoabsorption, and exciton emission from ZnO and other semiconductors as well