We present a detailed study on the optical properties of GaAsBi/GaAs multiple quantum well structure, optimized for the active area for vertical-external-cavity surface-emitting lasers. The quantum structure was grown by molecular beam epitaxy with every other barrier made thinner to have a homogeneous structure with high photoluminescence (PL) intensity. PL measurements were carried out in a wide temperature range from 4 to 300 K. The PL band of 1.085 eV was attributed to the optical transition in QWs with 8.0%Bi. The S-shaped temperature dependence of PL peak positions showed high localization effect of 30 meV. The internal quantum efficiency (IQE) was evaluated for the bismide structures with a modified ABB* method, which includes contribution from trap-assisted Auger recombination. The calculations showed low IQE of <0.025% for GaAs0.92Bi0.08/GaAs 12 QWs structure, which was explained by the low growth temperature, resulting in a high density of point defects in the material.

Fabry–Perot laser diodes based on (Al, Ga)As and Ga(As, Bi) with single or multiple parabolic or rectangular-shaped quantum wells (QWs) emitting at the 780–1100 nm spectral range were fabricated and investigated for optimization of the laser QW design and composition of QWs. The laser structures were grown using the molecular beam epitaxy (MBE) technique on the n-type GaAs(100) substrate. The photolithography process was performed to fabricate edge-emitting laser bars of 5 μm by 500 μm in size. The temperature-dependent power-current measurements showed that the characteristic threshold current of the fabricated LDs was in the 60–120 mA range. Light and current characteristics were almost linear up to (1.2–2.0) I_th. Low-frequency 10 Hz–20 kHz electrical and optical noise characteristics were measured in the temperature range from 70 K to 290 K and showed that the low-frequency optical and electrical noise spectra are comprised of 1/f and Lorentzian-type components. The positive cross-correlation between optical and electrical fluctuations was observed.

We explore quantum well laser diodes for applications in pulse oximetry based on two material systems, namely, classical AlGaAs and a rather exotic GaAsBi, with lasing at around 800 nm and 1100 nm, respectively. These spectral regions and material families were selected due to their closely matched effective penetration depths into soft tissue. An improved design of the band structure of device active areas was tested on both material systems, yielding enhancement of the two main parameters, namely, output power and threshold current. A maximum emission power of the AlGaAs laser diode was registered at 4.9 mW (I = 60 mA, λ = 801 nm). For the GaAsBi-based devices, the target emission of 1106 nm was measured in pulsed mode with a peak output power of 9.4 mW (I = 3 A). The most optimized structure was based on three GaAsBi quantum wells surrounded by parabolically graded AlGaAs barriers. This structure was capable of 130 mW peak power (I = 2 A, λ = 1025 nm) along with a more than tenfold decrease in threshold current to 250 mA compared to a classical rectangular quantum well active region.

The results of a study aimed at optimizing the optical properties of InGaAs quantum well structures by employing different barrier designs are presented. Single rectangular InGaAs quantum wells with approximately 21% indium and AlGaAs barriers, with different Al content 12, 20 and 30%, were theoretically modelled using the nextnano³ software to calculate band edges and levels in the quantum wells. A series of samples were grown using molecular beam epitaxy to clarify the influence of the Al fraction in the AlGaAs barriers on the optical properties of the quantum structures. Atomic force microscopy measurements were used to evaluate the surface roughness of the grown structures, while photoluminescence investigations provided insight into the optical quality and carrier confinement effects. The investigations revealed that the introduction of AlGaAs barriers resulted in an increased carrier confinement inside of the quantum well, but consequently resulted in the degradation of the InGaAs quantum well quality with the increase of aluminium content in the barrier. It was determined that a barrier with 12% of Al can be used to balance these effects, by providing a sufficient confinement, while retaining a satisfactory crystalline quality of the quantum structures.

In this study the emission homogeneity of InGaAs multiple quantum wells (MQW) was investigated. Two sets of samples grown by molecular beam epitaxy, with varying In content and QW thickness as well as barrier thickness, were mapped using room temperature photoluminescence and micro-photoluminescence. The result showed that increasing In content leads to a higher stress accumulation which can lead to the formation of a denser net of lattice mismatch dislocations in the QW layer. Samples with optimized barrier design exhibit uniform emission intensity.

In this study the emission homogeneity of InGaAs multiple quantum wells (MQW) was investigated. Two sets of samples grown by molecular beam epitaxy, with varying In content and QW thickness as well as barrier thickness, were mapped using room temperature photoluminescence and micro-photoluminescence. The result showed that increasing In content leads to a denser net of lattice mismatch dislocations in the QW layer. Samples with optimized barrier design exhibit uniform emission intensity.