Temperature Dependent Optical Band Gap Measurements of III-V Films by Low Temperature Photoluminescence Spectroscopy

Abstract

Photoluminescence (PL) spectroscopy is a powerful technique for probing the structures of many types of III-V semiconductor materials. When a semiconductor material is excited at a particular wavelength, electron-hole pairs are generated. The most intense radiative transition is between the conduction band and valence band, and this measurement is used to determine the material band gap. Radiative and non-radiative transitions in semiconductors also involve localized defect levels. The photoluminescence energy associated with these levels can be used to identify specific defects, and the amount of photoluminescence can be used to determine their concentration, and thus predict device quality. At ambient temperatures, the PL signal is typically broad, as much as 100 nm in width. When cooled, structural details may be resolved, and a small spectral shift between 2 samples may represent a change in a structural parameter. Thus a system with high spectral resolution is required.In this paper, a modular Low Temperature Photoluminescence system (LTPL) for measuring optical band gap as a function of temperature is described. Results show that the optical band gap shifts towards higher energy as the sample temperature decreases.

Effective Passivation of InGaAs Nanowires for Telecommunication Wavelength Optoelectronics

“…These growth conditions resulted in PL emission peaks at 1530, 1420, 1210, and 1120 nm at 80 K, from nanowires grown on patterns with a pitch size of 1 µm and a hole size of 80 nm. [ 12 ] Here, InGaAs nanowires with a PL emission peak at 1530 nm (at 80 K) were selected as a representative nanowire array to optimize the InP passivation shell growth, as the matching lattice constant of InGaAs with InP shell leads to the emission of 1550 nm at 80 K. [ 27 ] First, the nanowire core was passivated with an InP shell at the same temperature as InGaAs nanowire growth to avoid potential compositional change of the nanowire core and interdiffusion of core/shell interfaces at higher temperatures. Scanning electron microscopy (SEM) image of these nanowires ( Figure a) shows that the InP shell can be grown successfully at 600 °C; however, the uniformity of the nanowire array is reduced.…”

“…[30] Similarly, passivated nanowire arrays grown at 650 °C (Figure 3b) show a narrower emission peak at 1420 nm and an unvaried emission peak position. It has been reported that In 0.53 Ga 0.47 As with an emission wavelength at 1550 nm at 80 K, [27] is latticed matched to InP, resulting in a strain-free InGaAs/InP interface. [31] Here, the invariance of the emission peaks after passivation (Figure 3a,b) indicates a negligible strain at the InGaAs/InP interface at these core growth temperatures (600 and 650 °C).…”