Hall effect measurement of InAsN alloy films grown directly on GaAs(001) substrates by RF‐MBE

Abstract

Due to the huge bandgap-bowing, a red shift of the band gap energy with increasing nitrogen content is expected for the InAsN alloy. However, a blue shift of the fundamental absorption edge has been observed in a recent study. This result seems to be significantly affected by the Burstein-Moss effect because the InAsN alloy has a large carrier concentration. The Burstein-Moss effect should be ruled out in order to characterize the real band gap energy. In this paper, Hall effect measurements were performed to estimate the carrier concentration of the InAsN alloy films and the Burstein-Moss shift energy was evaluated. Excluding the Burstein-Moss shift energy, a red shift of the real band-gap energy with increasing nitrogen content was observed.1 Introduction The InAsN alloy has attractive potentials for infrared optical applications due to the huge bandgap-bowing [1] which is specific to the III-V-N-type ternary alloys. In our recent study, the InAsN epilayers were successfully grown on GaAs (001) substrates with a ~0.8 µm InAs buffer layer by RF-MBE, and the nitrogen content was estimated to be 0.09-1.69% [2]. Contrary to the theoretical prediction, a blue shift of the fundamental absorption edge was observed [3]. The result seems to be significantly affected by the Burstein-Moss (BM) effect because the InAsN alloy has a large carrier concentration due to its narrow bandgap. It will easily raise the absorption edge to higher energy than the real band gap energy. The BM shift energy (∆E BM ) should be excluded for determining the real band gap energy of InAsN.For this reason, we have attempted to evaluate the carrier concentration of the InAsN alloy films, which is the most important factor to estimate ∆E BM . The conductive buffer layer, such as a thick InAs buffer layer, is unfavourable for Hall effect measurements because it may cause carrier parallel conduction and conceal the information about the InAsN epilayers. In this work, the InAsN alloy films were grown directly on semi-insulating GaAs (001) substrates by RF-MBE. Next, the nitrogen content of all the samples was estimated by HR-XRD. The Hall effect measurements were carried out to characterize the carrier transport property and the FT-IR absorption measurements were performed to obtain the optical absorption spectra.

Photoluminescence spectroscopy of bandgap reduction in dilute InNAs alloys

“…This increase of electron concentration with increasing nitrogen content has been observed by Hall measurements of InNAs films grown on semiinsulating GaAs substrates by molecular-beam epitaxy ͑MBE͒. 8 Therefore, the nitrogen-induced band gap reduction in InNAs can generally only be estimated from absorption spectroscopy once the contribution of Moss-Burstein shift to the position of the absorption edge has been modeled. [7][8][9] In this letter, the temperature dependence of photoluminescence ͑PL͒ from dilute InNAs films grown by MBE is reported.…”

“…3,4 While a great deal of attention has been paid to GaNAs and GaInNAs alloys for nearinfrared applications, the investigation of related dilute nitride alloys, such as GaNSb ͑Ref. 5͒ and InNAs, [6][7][8][9] for midinfrared applications is only in its infancy. Indeed, band gap reduction has proved difficult to observe unambiguously in absorption spectra from InNAs alloys.…”

“…Indeed, band gap reduction has proved difficult to observe unambiguously in absorption spectra from InNAs alloys. [7][8][9] The reduction of the absorption-edge energy with increasing nitrogen content has so far only been observed in one optical absorption study of InNAs alloys. 6 Generally, absorption edges at higher energies than the true band gap are observed in n-type InNAs epilayers.…”

“…6 Generally, absorption edges at higher energies than the true band gap are observed in n-type InNAs epilayers. [7][8][9] This is due to the Moss-Burstein effect, 10,11 resulting from band filling due to unintentionally degenerate n-type doping in the InNAs alloy. This proclivity of InAs and InNAs for n-type conductivity is consistent with the amphoteric defect model.…”

“…8 Therefore, the nitrogen-induced band gap reduction in InNAs can generally only be estimated from absorption spectroscopy once the contribution of Moss-Burstein shift to the position of the absorption edge has been modeled. [7][8][9] In this letter, the temperature dependence of photoluminescence ͑PL͒ from dilute InNAs films grown by MBE is reported. The PL spectra unambiguously show band gap reduction with increasing N content.…”