Effect of number of quantum wells on the operational and spectral characteristics of strained InGaAs semiconductor laser diode

Abstract Bio-photonic and optical communications applications require infrared semiconductor lasers in the range of 0.8–1.2 μm, and InGaAs quantum well (QW) lasers are good candidates to cover these wavelengths. The number of wells in QW lasers plays a pivotal role in their operation and spectral properties. In this paper, the role of the number of wells in highly-strained InGaAs QW lasers is experimentally studied. In this framework, single, double, and triple InGaAs QW lasers were fabricated and prepared with 800 μm length and 45 μm oxide width. The transmission electron microscope, photoluminescence (PL), quantum efficiency <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">ext</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> , wall-plug efficiency <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">wp</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> , threshold current density ( J th ), emission wavelength, optical gain, and nearfield profiles were recorded. The J th exhibited a tangible increase which was found to be 252, 275, and 292 A cm −2 for single, double, and triple laser samples, respectively. Meanwhile, t <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">ext</mml:mi> </mml:mrow> </mml:msub> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">wp</mml:mi> </mml:mrow> </mml:msub> </mml:math> decrease when the number of QWs is increased. Emission spectra revealed that the central wavelength increased with the increasing number of wells to be 1.172, 1.184, and 1.197 μm for single, double, and triple laser samples, respectively. This redshift is also found in PL. Optical gain measurements showed an increase in the breadth of the gain and a decrease in the internal optical losses, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>i</mml:mi> </mml:mrow> </mml:msub> </mml:math> , as the number of wells increased. The 3D nearfield images revealed an increase in profile in both x-and y-directions when the number of wells increased, which is attributed to the increase of the active region thickness with the increasing number of wells. This study confirms the potential to modify the properties of infrared semiconductor lasers by opting for an adequate number of wells in the active region to meet the specific needs of modern photonic applications.