Experimental and modelling study of InGaBiAs/InP alloys with up to 5.8% Bi, and with Δ_so> E_g

Temperature dependent photo-modulated reflectance is used to measure the band gap E_g and spin-orbit splitting energy Δ_so in dilute-Bi In_0.53Ga_0.47As_1-xBi_x/InP for 1.2% ≤ x ≤ 5.8%. At room temperature, E_g decreases with increasing Bi from 0.65 to 0.47 eV (∼2.6 μm), while Δ_so increases from 0.42 to 0.62 eV, leading to a crossover between E_g and Δ_so around 3.8% Bi. The 5.8% Bi sample is the first example of this alloy where Δ_so > E_g has been confirmed at all temperatures. The condition Δ_so > E_g is important for suppressing hot-hole-producing non-radiative Auger recombination and inter-valence band absorption losses and so holds promise for the development of mid-infra-red devices based on this material system. The measured variations of E_g and Δ_so as a function of Bi content at 300 K are compared to those calculated using a 12-band k.p Hamiltonian which includes valence band anti-crossing effects. The E_g results as a function of temperature are fitted with the Bose-Einstein model. We also look for evidence to support the prediction that E_g in dilute bismides may show a reduced temperature sensitivity, but find no clear indication of that.