Pressure-induced resonance Raman effect of InAs x P1−x alloy films on InP

Abstract

We have studied the effect of hydrostatic pressure on the Raman spectra of InAsxP1−x alloy films grown on InP substrates. High-pressure Raman scattering provides very useful information on the microscopic properties of the materials because the electronic transition can be controlled by using the pressure. The samples with intermediate compositions (0 < x < 1) exhibit both InAs-like and InP-like modes at all the pressures (up to ∼80 kbar) we tried. Pressure is well known to increase the magnitude of the E1 band gap whose magnitude is responsible for the Raman scattering efficiency of materials such as InP and GenSim multiple quantum wells. Using the 457.9 nm (2.708 eV) line of an argon ion laser, we could observe enhanced Raman scattering efficiency for the x = 0.7, x = 0.75, and x = 0.8 alloys at certain pressures, which indicates that the three samples have E1 band gaps below 2.708 eV at ambient pressure. (Notice that both InAs-like and InP-like modes show resonance features). This result is consistent with the measurement of the electronic structure by using ellipsometry. The shift rates of the E1 band gaps of the three samples are comparable to that of InP. The resonance of ternary alloys with wider widths than InAs indicates that they have spatially fluctuating E1 band gaps, although good electronic band structures are maintained.