Exciton binding energy and electron effective-mass in strain compensated InGaAsN/GaAs single Quantum Well

Abstract

An electron effective mass (m e *) of (0.11±0.015)m 0 is experimentally determined in high Indium content InGaAsN quantum well. The impact of the large m e * in the material differential gain is analyzed through a gain model.InGaAsN/GaAs has attracted intense attention ever since it was suggested as a compound semiconductor material system for the realization of high-performance laser diodes emitting at the 1.3 and 1.55 µm optical fiber window. Recently high-performance 1.3µm InGaAsN QW lasers with very low threshold current density have been demonstrated [1,2], under the strategy of maximizing the indium concentration to the limit imposed by compressive strain and adding the minimum amount of nitrogen to lower the bandgap to ~ 0.95 eV. Despite the recent laser successes, many fundamental physical parameters of InGaAsN are still virtually unknown. For instance, to date no direct determination of the electron effective mass, m e *, has been reported for high Indium content (~30-40%) In x Ga 1-x As y N 1-y-, due to the difficulties in growing thick freestanding epilayers (typically ~1-3 µm). Model calculations predict an increase in m e * when nitrogen is added to the InGaAs host[3,4] but the magnitude of this increase is significantly different. Furthermore, these theoretical models are not in agreement on how m e * affects the performance of laser diodes, especially in the prediction of the peak differential gain dG/dN [5].In this paper we perform a detailed line shape analysis of the temperature dependent Photoluminescence (PL) spectra of a In 0.4 Ga 0.6 As 1-y N y /GaAs single quantum well (y=0; 0.005) to experimentally determine the e1-hh1 exciton binding energy, and from there derive the conduction band-edge effective mass, m e *. The samples studied here are grown by low-pressure (200 mbar) and low temperature (530 0 C) metal-organic chemical vapor deposition (MOCVD) [1]. The width of the QW is 6-nm and the thickness of the GaAs barrier is 300-nm.Partial strain compensation of the highly compressively strained QW is achieved by utilizing two 7.5nm-thick GaAs 0.85 P 0.15 tensile strain layers offset 10nm from the QW, and a tensile strain buffer layer of GaAs 0.67 P 0.33 . PL measurements were carried out with the samples mounted on the cold finger of a closed-cycle Helium cryostat that allows varying the temperature from 10K to 300K. PL was excited by a mode-locked Ti:Sapphire laser emitting 800nm pulses with 100fs duration and 82MHz repetition rate. Typical average excitation intensity on the sample was 0.5W/cm 2 , corresponding to a photo-excited carrier density in the experiments of 2×10 10 cm -2 .The PL spectra at different temperatures were fitted assuming a superposition of both excitonic and free carrier recombination (figure 1). From the fit, the temperature evolution of the relative contribution from free carriers and free excitons to the radiative recombination was assessed by integrating the corresponding areas of the exciton and free carrier peaks, respectively. From a plot of the ratio between th...