Investigation of the optical modal gain in an InAsP/AlGaInP quantum dot laser diode structure

Abstract

The light–current (L–I) and current–voltage (I–V) characteristics of self-assembled InAsP/AlGaInP quantum dots grown by organometallic vapor-phase epitaxy were measured over a temperature range of 160–400 K. The investigated samples had different cavity lengths (1, 2, 3, and 4 mm). Our results show that the threshold current decreases with increasing cavity length. The lower threshold current density was 212 A/cm², which corresponds to a cavity length of 4 mm. Moreover, the threshold modal gains for various stripe cavity lengths were investigated at room temperature. The longest cavity (4 mm) consisted of many dots; therefore, it easily reached the threshold modal gain of 6.5 cm⁻¹. The temperature dependence of the threshold current density (J_th) was investigated. It was found that J_th increased with increasing temperature and it increases faster at high operating temperatures. A 4 mm device is less temperature dependent with T₀ ≈ 83 K when operated between 320 and 360 K. The emission spectra exhibited a redshift of approximately 14 nm when the cavity length increased from 1 to 4 mm. The ideality factor and series resistance of the diode laser structures decrease with increasing temperature.