C. Fuchs

Novel type-II material system for laser applications in the near-infrared regime

The design and experimental realization of a type-II W-multiple quantum well heterostructure for emission in the λ > 1.2u2009μm range is presented. The experimental photoluminescence spectra for different excitation intensities are analyzed using microscopic quantum theory. On the basis of the good theory-experiment agreement, the gain properties of the system are computed using the semiconductor Bloch equations. Gain values comparable to those of type-I systems are obtained.

Type-II vertical-external-cavity surface-emitting laser with Watt level output powers at 1.2 μm

Semiconductor laser characteristics based on type-II band-aligned quantum well heterostructures for the emission at 1.2u2009μm are presented. Ten “W”-quantum wells consisting of GaAs/(GaIn)As/Ga(AsSb)/(GaIn)As/GaAs are arranged as resonant periodic gain in a vertical-external-cavity surface-emitting laser. Its structure is analyzed by X-ray diffraction, photoluminescence, and reflectance measurements. The lasers power curves and spectra are investigated. Output powers at Watt level are achieved, with a maximum output power of 4u2009W. It is confirmed that laser operation only involves the type-II transition. A blue shift of the material gain is observed while the modal gain exhibits a red shift.

Excitonic transitions in highly efficient (GaIn)As/Ga(AsSb) type-II quantum-well structures

The excitonic transitions of the type-II (GaIn)As/Ga(AsSb) gain medium of a “W”-laser structure are characterized experimentally by modulation spectroscopy and analyzed using microscopic quantum theory. On the basis of the very good agreement between the measured and calculated photoreflectivity, the type-I or type-II character of the observable excitonic transitions is identified. Whereas the energetically lowest three transitions exhibit type-II character, the subsequent energetically higher transitions possess type-I character with much stronger dipole moments. Despite the type-II character, the quantum-well structure exhibits a bright luminescence.

Gain spectroscopy of a type-II VECSEL chip

Using optical pump–white light probe spectroscopy, the gain dynamics is investigated for a vertical-external-cavity surface-emitting laser chip, which is based on a type-II heterostructure. The active region of the chip consists of a GaAs/(GaIn)As/Ga(AsSb)/(GaIn)As/GaAs multiple quantum well. For this structure, a fully microscopic theory predicts a modal room temperature gain at a wavelength of 1170u2009nm, which is confirmed by the experimental spectra. The results show a gain buildup on the type-II chip that is delayed relative to that of a type-I chip. This slower gain dynamics is attributed to a diminished cooling rate arising from the reduced electron–hole scattering.

Atomic structure of ‘W’‐type quantum well heterostructures investigated by aberration‐corrected STEM

The atomic structure of (GaIn)As/Ga(AsSb)/(GaIn)As‐‘W’‐type quantum well heterostructures (‘W’‐QWHs) is investigated by scanning transmission electron microscopy (STEM). These structures were grown by metal organic vapour phase epitaxy and are built for type‐II laser systems in the infrared wavelength regime. For two samples grown at 525°C and 550°C, intensity profiles are extracted from the STEM images for each sublattice separately. These intensity profiles are compared to the one obtained from an image simulation of an ideal ‘W’‐QWH that is modelled in close agreement with the experiment. From the intensity profiles, the width of the different quantum wells (QWs) can be determined. Additionally, characteristics connected to the growth of the structures, such as segregation coefficients and material homogeneity, are calculated. Finally, composition profiles are derived from the STEM intensity profiles to a first approximation. For these composition profiles, the expected photoluminescence (PL) is computed based using the semiconductor luminescence equations. The PL spectra are then compared to experimental measurements for both samples.

High-temperature operation of electrical injection type-II (GaIn)As/Ga(AsSb)/(GaIn)As “W”-quantum well lasers emitting at 1.3 µm

Electrical injection lasers emitting in the 1.3u2009μm wavelength regime based on (GaIn)As/Ga(AsSb)/(GaIn)As type-II double “W”-quantum well heterostructures grown on GaAs substrate are demonstrated. The structure is designed by applying a fully microscopic theory and fabricated using metal organic vapor phase epitaxy. Temperature-dependent electroluminescence measurements as well as broad-area edge-emitting laser studies are carried out in order to characterize the resulting devices. Laser emission based on the fundamental type-II transition is demonstrated for a 975u2009μm long laser bar in the temperature range between 10u2009°C and 100u2009°C. The device exhibits a differential efficiency of 41u2009% and a threshold current density of 1.0u2009kA/cm2 at room temperature. Temperature-dependent laser studies reveal characteristic temperatures of T0u2009=u2009(132u2009±u20093)u2009K over the whole temperature range and T1u2009=u2009(159u2009±u200913)u2009K between 10u2009°C and 70u2009°C and T1u2009=u2009(40u2009±u20091)u2009K between 80u2009°C and 100u2009°C.

Author Correction: High-temperature operation of electrical injection type-II (GaIn)As/Ga(AsSb)/(GaIn)As “W”-quantum well lasers emitting at 1.3 µm

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Band offset in (Ga, In)As/Ga(As, Sb) heterostructures

A series of (Ga, In)As/GaAs/Ga(As, Sb) multi-quantum well heterostructures is analyzed using temperature- and power-dependent photoluminescence (PL) spectroscopy. Pronounced PL variations with sample temperature are observed and analyzed using microscopic many-body theory and band structure calculations based on the k⋅p method. This theory-experiment comparison reveals an unusual, temperature dependent variation of the band alignment between the (Ga, In)As and Ga(As, Sb) quantum wells.