R. Schwedler

Observation of Bloch oscillations in a semiconductor superlattice

We report unambiguous experimental evidence for electron Bloch oscillations: The transient four-wave mixing signal of a biased semiconductor superlattice shows a periodic modulation with a time constant expected from Bloch oscillation theory. The oscillation frequency can be tuned over 400% with the applied electric field. The electron performs up to four oscillation cycles before the coherence is lost.

Optical characterization of strained InGaAs/InP quantum well structures

The effects of strain on the optical properties of In<inf>1-x</inf>Ga<inf>x</inf> As/InP multiple-quantum well structures grown by low pressure metal organic vapor phase epitaxy have been investigated by photoluminescence spectroscopy. The investigated composition range is varied between 0.17 < x<inf>Ga</inf> < 1.00. Sputtered neutrals mass spectrometry has been used to calibrate the growth interpolated nominal compositions. Distinct peaks from monolayer variations of well thickness are observed from all samples. The analysis of the PL-spectra leads to the assumption of an intermediate layer of InAs<inf>0.65</inf>P<inf>0.35</inf> at the InP to In<inf>1=x</inf> Ga<inf>x</inf> As (lower) interface.

Ultrafast carrier dynamics in in1−x ga x as/inp heterostructures

We investigate carrier capture and carrier transport in the InGaAs/InP material system by luminescence spectroscopy with femtosecond time resolution. Comparative studies are performed on samples of different well width, barrier width and gallium mole fraction of the InGaAs layers. The investigations focus on excitation conditions that are comparable to those for semiconductor laser operation. Firm data on carrier dynamics are presented for these conditions. We find that the overall transfer rates of electrons and holes are similar and independent of well width. Furthermore, the transfer times show a linear dependence on barrier width. From experimental and model calculation results we derive some guidelines for the design of high-frequency laser devices.

Growth and characterization of In0.53Ga0.47As/InxGa1−xAs strained-layer superlattices

Abstract Since the early proposal that InGaAs/InGaAs strained-layer superlattices (SLSs) should constitute a new class of optoelectronic materials, very little work has been done to master the growth conditions and optimize the resulting superlattice properties. In this work, we present the results of a preliminary investigation of SLSs grown by low-pressure metal-organic vapour phase epitaxy. Two different series of samples were grown to check independently the effect of well thickness and barrier composition. In both cases, in order to conserve one layer nominally lattice-matched to InP, the wells had a standard composition In0.53Ga0.47As.

Type-I and type-II Wannier-Stark effect in InGaAs/InGaAs superlattices

The formation of minibands is demonstrated in photocurrent experiments on shallow In0.53Ga0.47As/In0.40Ga0.60 As superlattices grown by low-pressure metal-organic vapor-phase epitaxy. Field-dependent variations of the spectral shape are attributed to Wanner-Stark localization. Both type-I transitions between electrons and heavy holes and type-II transitions involving light holes confined in the In0.40Ga0.60 As layers are observed and distinguished by their characteristic field dependence.

Ultrafast carrier transport and capture in InGaAs/InP heterostructures

The carrier dynamics in InGaAs/InP heterostructures is studied with luminescence up-conversion spectroscopy with 300 fs time resolution. A comparative study using samples with different well and barrier thicknesses is performed to separate the carrier transport across the InP barriers to the quantum wells (QWs) and the final carrier capture into confined states of the quantum wells. Samples with different Ga-content of the InGaAs QW layers are also investigated. The capture times are virtually independent of well width. Local capture time constants of about 800 fs for electrons and 200 fs for holes are determined by model calculations. It is concluded that the modulation frequency of devices up to 300 GHz is not limited by the charge transfer from barriers to wells.<<ETX>>

Quantitative comparison of mass spectrometry and photoluminescence on InAsP/InP multiple quantum well structures

Abstract We report a direct comparison of low-temperature photoluminescence spectroscopy and sputtered neutral mass spectrometry on an asymmetric InAsP/InP multiple quantum well structure. Distinct luminescence peaks from all quantum well layers were observed. They were unambiguously assigned to individual quantum well layers by subsequent sputter etching steps. Based on mass spectrometry data, numerical calculations of the luminescence transitions were performed without any free parameters. The consequences of the excellent agreement between the experimental and modelled photoluminescence data are discussed.

Optical characterization of indium-rich strained In1−xGaxAs/InP single- and multiple-quantum-well structures

Abstract We report on the photoluminescence spectroscopy of a large set of strained In 1− x Ga x As/InP quantum well structures grown by low pressure metallo-organic vapour phase epitaxy. Distinct peaks from monolayer steps are observed in all samples. For the first time, data on indium-rich In 1− x Ga x As/InP structures with complementary gallium contents as low as x Ga = 0.07 and x Ga = 0.11 are reported. The sample quality appears independent of the number of quantum wells stacked in the structure. With decreasing gallium content, a decrease in luminescence intensity is observed, which is related to an increase in the number of non-radiative recombination centres with respect to lattice-matched samples.