Hydrostatic pressure dependence of the fundamental bandgap of InN and In-rich group III nitride alloys

Abstract

We report studies of the hydrostatic pressure dependence of the fundamental bandgap of InN, In-rich In 1-x Ga x N (0 < x < 0.5) and In 1-x Al x N (x = 0.25) alloys. The bandgap shift with pressure was measured by optical absorption experiments with samples mounted in diamond anvil cells. The pressure coefficient is found to be 3.0±0.1 meV/kbar for InN. A comparison between our results and previously reported theoretical calculations is presented and discussed. Together with previous experimental results, our data suggest that the pressure coefficients of group-III nitride alloys have only a weak dependence on the alloy composition. The photoluminescence signals appear to yield significantly smaller pressure coefficients than the bandgap from absorption measurements. This is due to emission associated with highly localized states. Based on these results, the absolute deformation potentials of the conduction and valence band edges are estimated.

Electronic Band Structure of InxGa1-xN under Pressure

“…Starting from the value of 39 meV/GPa for GaN we observe a very strong decrease in the band gap pressure coefficient up to x ≈ 0.25; then it decreases more slowly, having at x = 0.50 the value 26 meV/GPa, essentially as in pure InN, 27 meV/GPa, as we estimate our calculational error to be about ±1 meV/GPa. Our calculated pressure coefficients for varying In content are in good agreement with the experimental data obtained from absorption measurements [3], where similar tendencies are observed. It is suggestive to associate a strong nonlinear behavior of the band gap pressure coefficient of InGaN with In-induced changes of the states at the valence band top [5].…”

“…The composition dependence of the In x Ga 1−x N gap bowing was obtained by Bechstedt et al [21], where the calculated values for wurtzite In x Ga 1−x N vary between 2.5 and 1.5 eV within the interval 0 ≤ x ≤ 0.25 and decrease further to 1.4 eV for x = 0.5 and 1.3 eV for x = 0.75. On the other hand, constant band gap bowing parameters were reported by Li et al [22] (b = 1.43 eV) and by Kuo et al [20] (b = 1.89 eV).…”

“…We adjusted the fundamental band gaps at the Γ point to the experimental values, for GaN: 3.28 eV [18] and for InN: 0.62 eV, which is an average of the values found in the literature (0.60-0.65 eV) [1][2][3][4]. Then we obtained the band structure of InGaN using the same external potential parameters for real atoms and empty spheres as determined for GaN and InN by the adjusting procedure.…”

“…Then, some experiments performed on high quality samples with low free-electron concentration, mostly grown by molecular beam epitaxy (MBE), revealed that the fundamental gap is much smaller. Recently, optical studies at room temperature showed that the InN gap is in the range of 0.6-0.7 eV [1][2][3][4]. The discovery of the low band gap of InN has extended the range of available direct band gaps of In x Ga 1−x N alloys into the near-infrared part of the spectrum, causing an increased interest in these alloys.…”

Strain effects in group-III nitrides: Deformation potentials for AlN, GaN, and InN

“…10,11,[14][15][16][17] For AlN and InN no experimental data are available, except for the hydrostatic deformation potential of the band gap in InN. 18 Previous theoretical studies have also produced widely differing values, resulting in a large uncertainty range. [19][20][21] The error bars can, in part, be attributed to the band-gap problem of density functional theory (DFT) in the local-density or generalized gradient approximations (LDA and GGA).…”