Influence of pressure on the optical properties of InxGa1-xN epilayers andquantum structures - art. no. 115319

The influence of hydrostatic pressure on the emission and absorption spectr a measured for various types of InGaN structures (epilayers, quantum wells, and quantum dots) is studied. While the known pressure coefficients of the GaN and InN band gaps are about 40 and 25 meV/GPa, respectively, the obser ved pressure-induced shifts in light emission energy in the InGaN alloys di ffer significantly from concentration-interpolated values. With increasing In concentration, and thus decreasing emission energy, the observed pressur e coefficients become very small, reaching zero for emission energies simil ar to2 eV (roughly the value of the InN band gap). On the other hand, the p ressure coefficient derived from absorption experiments exhibit a much smal ler decrease with decreasing energy when referred to the same scale as the emission data. First-principles calculations of InGaN band structures and t heir modification with pressure are performed. The results are not able to explain the huge effect observed in the emission experiments, but they are in good agreement with the optical absorption data. Significant bowings of the band gap and its pressure coefficients are found, and they are especial ly large for small In concentrations. This behavior is related to the chang es in the upper valence band states due to In alloying. Some possible mecha nisms are discussed which might be expected to account for the low pressure coefficients of the light emission energy and the difference between the s ensitivity of the emission and absorption to pressure.