Reabsorption, band-gap narrowing, and the reconciliation of photoluminescence spectra with electrical measurements for epitaxial n-InP

Abstract

The effects of reabsorption and band-gap narrowing (BGN) on experimental photoluminescence (PL) spectra of n-InP grown by metalorganic chemical vapor deposition are analyzed. PL spectra show a pronounced widening of the main PL peak and a shift of that peak to higher photon energy with increasing doping due to band filling. However, the magnitude of these effects, both here and in earlier studies of n-type III–V semiconductors, is smaller than expected based upon band filling calculations and electrical measurements. Various explanations for these discrepancies between PL spectra and band filling calculations have been proposed, but little experimental support is currently available. In this article we demonstrate unambiguously that both the n-InP PL peak width and the peak position are significantly reduced by reabsorption, and that reabsorption completely explains the observed discrepancy between the measured PL peak width and the calculated band filling based on electrical measurements. In particular, we show that reabsorption must be accounted for when extracting the Fermi level from experimental n-InP PL spectra, otherwise the Fermi level value is severely underestimated. Since previous studies of the n-InP PL line shape have neglected reabsorption and instead attributed the unexpectedly low extracted Fermi level value to band-gap narrowing effects, we reinvestigate BGN in n-InP by considering only the low-energy tail of the PL spectra. The extent of the low-energy band tail below the intrinsic band-gap energy is observed to be only about half as large as n-InP BGN predicted theoretically. Very similar results have been reported in the literature for n-GaAs and is either due to an overestimation of the BGN by theory or a failure of PL to reflect the full extent of a highly nonrigid BGN shift. In regard to the latter, we demonstrate that a highly nonrigid BGN shift does indeed exist for n-InP, with the BGN shift near zone center being at least three times larger than the energy shift of states near the Fermi surface for n=4×1018 cm−3.

Si incorporation and Burstein–Moss shift in n-type GaAs

“…The discrepancy of BGN between the experimental result and the Jain theory is clearly seen at high doping level. Very similar discrepancies have been observed for n-InP [48]. Sieg and Ringel [48] have given three possible explanations in the case of n-GaAs and n-InP between the theoretical BGN calculated from Eq.…”

“…Very similar discrepancies have been observed for n-InP [48]. Sieg and Ringel [48] have given three possible explanations in the case of n-GaAs and n-InP between the theoretical BGN calculated from Eq. (10) and experimental BGN obtained by PL.…”

“…(10) giving much larger BGN values than have been observed experimentally by PL. A similar discrepancy occurs even in n-InP [48].…”

Growth and optical properties of high-density InN nanodots

“…In addition, Fu et al [16] provide a convenient 1 m formula to determine free-electron concentration in InN films by PL measurement. The relationship between FWHM and freeelectron concentration can be well described by the empirical formula [17,18]. The free electron concentration was estimated as $7 Â 10 18 and $2 Â 10 19 cm À 3 , respectively, for the CM and PM growth of InN nanodots.…”

A review of InP/InAlAs/InGaAs based transistors for high frequency applications

“…Both thermionic and tunneling currents are exponentially related to built in potential. It is found that the BGN in n-InP is higher than that of n-GaAs [120]. The BGN in AlAs and GaP are higher than that of InP, GaAs and InAs due to higher conduction band density of states and lower relative permittivity of these materials [112,121].…”