InGaAs Multiple Quantum Wells Research Articles

Normal incidence intersubband transitions in Si-doped InGaAs multiple quantum wells

Angle- and polarization-resolved infrared techniques have been used to study the polarization selection rules of intersubband transitions in Si-doped InGaAs multiple quantum wells (MQWs). Intersubband transitions are found to be active for light, polarized both parallel and perpendicular to the MQW plane, and to show a strain dependent splitting between the corresponding transition energies. Previously reported intersubband data measured in the Brewster angle configuration for the same lattice-matched and strained Si-doped InGaAs MQWs were also reproduced.

Determination of the layer structure of embedded strained InGaAs multiple quantum wells by high resolution x-ray diffraction

High resolution x-ray diffraction (HRXRD) has been used to determine the layer compositions and thicknesses of compressively strained InGaAs multiple-quantum-well (MQW) structures embedded in thick cladding layers that are nominally lattice matched to InP. The entire layer structure was accurately determined from the results of HRXRD measurements for a simple strained MQW structure in which barriers and claddings are of the same composition. The estimated margins of error are less than 1% for the quantum-well indium composition and ±2.5 Å for well and barrier thicknesses. The layer structure of the active region in a complete InGaAlAs graded-index separate confinement strained MQW laser diode has also been determined by HRXRD.

Low-pressure MOVPE growth and characterization of strained-layer InGaAs-InGaAsP quantum well lasers

High-quality strained-layer In x Ga 1- x As-InP quantum well structures, as revealed by photoluminescence and transmission electron microscopy studies, were grown by low-pressure metalorganic vapour phase epitaxy (MOVPE). Laser diodes at 1.5 μm wavelength employing compressively as well as tensile strained In x Ga 1- x As-InGaAsP quantum wells with better performance than the much more extensively studied bulk InGaAsP and unstrained quantum well lasers are demonstrated. Threshold current densities as low as 92 and 147 A/cm 2 were measured from tensile and compressively strained single quantum well lasers. For both signs of the strain, 0.8 mA threshold current operation is achieved of all-MOVPE grown semi-insulating planar buried heterostructure (SIPBH) lasers. These data represent, to the best of our knowledge, the lowest values reported so far for 1.5 μm wavelength lasers grown by any technique. Compressively strained multiple quantum well (MQW) lasers are found to excel in high power operation, as demonstrated by the record CW output power of 325 mW, resulting from improved threshold current, temperature sensitivity of the threshold current and external differential efficiency. The tensile strained MQW lasers show very high differential and total gain, resulting in very high operating temperature up to 140°C. Three-section distributed feedback lasers employing a compressively strained InGaAs MQW active region showed very large wavelength tuning ranges as high as 7.2 nm with a minimum linewidth as low as 700 kHz.

Intervalence band absorption in strained and unstrained InGaAs multiple quantum well structures

We report the direct determination of absorption losses in unstrained InGaAs/InGaAsP and InGaAs/InGaAlAs and strained InGaAs/InGaAsP layer multiple quantum well (MQW) laser structures. In the case of the unstrained structures we find a strong dependence of the absorption on carrier density indicating the presence of an intrinsic optical loss mechanism, the intervalence band absorption (IVBA). In the strained layer InGaAs/InGaAsP structures, IVBA is completely switched off. Our results explain the superiority of strained layer InGaAs MQW lasers.

Strained-layer InGaAs-GaAs-AlGaAs lasers grown by molecular beam epitaxy for high-speed modulation

A study of strained InGaAs quantum wells grown on GaAs by molecular beam epitaxy was performed in order to optimize the growth conditions for strained-layer single- and multiple-quantum-well lasers. Photoluminescence of the quantum wells shows a rapid degradation in material quality as the substrate temperature is reduced below 500 degrees C. Single-quantum-well (SQW) laser structures contain a 55 AA 35% InGaAs quantum well, while multiple-quantum-well (MQW) lasers contain four 25% or 35% InAs mole fraction 55 AA quantum wells. The 35% SQW lasers emit at 1.06 mu m, while the 25% InGaAs MQW lasers emit at 1.07 mu m. The SQW lasers have threshold current densities as low as 83 A/cm/sup 2/ for 150*1000 mu m devices. Microwave modulation bandwidths increase with an increasing In mole fraction and number of quantum wells, as predicted by theory. A differential gain of 5.0*10/sup -15/ cm/sup 2/ is calculated from the microwave response measurements for the 35% MQW devices. >