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Programm und Abstracts der Sitzung HL 9

Sputter depth profiling of GaN/InAlGaN multi quantum well structures

•Gernot Ecke¹, Rastislav Kosiba¹, Gabriel Kittler¹, Nikos Pelekanos² und Oliver Ambacher^1
1Center of Micro- and Nanotechnologies, TU Ilmenau, D-98693 Ilmenau, Germany
²Foundation for Research and Technology - Hellas, P.O. Box 1527, GR 71110 Heraklion, Crete, Greece

Multi quantum well (MQW) structures play a crucial role in the design of many optoelectronic devices. The regularity of these structures, the composition of the layers, and the quality of the interfaces between the layers are very important for the device functionality. In this contribution, the sputter depth profiles across the MQW consisting of seven GaN/InAlGaN layer pairs with thickness of 7 nm will be presented. The sputter depth profiling was carried out by Auger electron spectroscopy in conjunction with argon ion sputtering. Grazing incidence and low ion energy provided good sputtering conditions for highly depth resolved measurements. For the evaluation of the depth profiles the factor analysis of the nitrogen KLL and overlapping Al LMM and Ga MNN Auger transitions was applied. The deterioration of the true depth profile due to the sputtering itself as well as due to the information depth of the Auger electrons was followed by the dynamic Monte Carlo simulation code TRIDYN. From the good agreement between the measurement and the simulation the regularity of the measured MQW structure as well as good interface quality could be proven.

Time-domain THz spectroscopy of electronic exitations in GaAs/AlGaAs superlattices

•André Dreyhaupt, Stephan Winnerl, Thomas Dekorsy und Manfred Helm
Institut für Ionenstrahlphysik und Materialforschung, Forschungszentrum Rossendorf, Postfach 51 01 19, 01314 Dresden

We investigate the electronic properties of weakly and more strongly coupled n-doped GaAs/AlGaAs superlattices by time-domain THz spectroscopy in the low frequency range from about 0.5 to 3.5 THz. The sample properties are modulated either by applying an AC voltage via a gate electrode or by injecting a vertical current. The transmission signal is detected at the frequency of the modulation voltage with a lock-in amplifier leading to a signal-to-noise ratio superior compared to conventional FTIR spectroscopy in this frequency range. We will discuss the observation of inter-miniband transitions, confined donor transitions, plasmon excitations and the measurement of intra-miniband THz conductivity in a wide range of lattice temperatures.

Dynamics of Excitons in Coupled Quantum Well Structures

•Andreas Gärtner¹, D. Schuh² und J. P. Kotthaus^1
1CeNS und Sektion Physik der LMU, München
²Walter Schottky Institut, TU München

The experiments to learn more about motion and interaction of long-living excitons in coupled quantum wells (QW) [1] are carried out in semiconductor heterostructures at low temperatures (4 K). These epitaxially grown samples contain two GaAs-QWs which are separated by a thin tunnelling barrier.

Metallic gates applied to a sample generate an electrical field perpendicular to the QW layers. This causes the transition from direct to spatially indirect excitons, i.e. electron and hole are located in different QWs. Thus, the overlap of their wave functions is reduced and the excitonic life time increases.
By means of the quantum confined stark effect (QCSE) the vertical electric field affects the effective excitonic potential [2]. It can be modulated by interdigitated gate structures [3] leading to in-plane dift phenomena.

In our experimental pump-and-probe-setup we observed these effects on photo generated excitons by analyzing their emitted photoluminescence spatially, temporally and spectrally. An intensified CCD-Camera featuring a temporal resolution in the sub-nanosecond regime allows further detailed studies on the dynamics of excitonic drift.

[1] Butov et al., Nature 417, 47 (2002)

[2] S. Zimmermann et al., Phys. Rev. B 56, 13414 (1997)

[3] J. Krauß et al., Phys. Rev. Lett. 88, 036803 (2002)

Piezo-electric fields in InGaAsP induced by spontaneous self-ordering

•S. Krämer¹, G. H. Döhler¹, S. Neumann², W. Prost² und T. J. Tegude^2
1Institut für Technische Physik I, Universität Erlangen-Nürnberg, Erwin-Rommel-Str. 1, D-91058 Erlangen
²Fachbereich Halbleitertechnik/Halbleitertechnologie, Universität Duisburg, Lotharstr. 55 LT, D-47048 Duisburg

InGaAsP grown by MOCVD under specific growth conditions form a monolayer superlattice along the [111] B direction (ßpontaneous self-ordering). This superlattice can be formed by InP-GaAs or InAs-GaP. Because of the different bond lengths in these combinations the resulting two versions of InGaAsP would have varying distances between the alternating layers compared to unstrained bulk material. For InGaAsP, grown lattice matched on an InP-substrate, these different layer sequences lead to significant piezo-electric fields in the range of about 100 kV/cm. The existence of order-induced piezo-electric fields for ordered GaInP, lattice matched to GaAs, has been discussed controversially in the literature [1], [2], [3]. To investigate the occurrence, sign, and magnitude of piezo-electric fields in the InGaAsP-system, we embedded an InGaAsP - quantum well in an InP - pin and - nip structure, respectively. By observing the quantum confined Stark effect in the photocurrent signal in both structures we were able to determine the strength (and sign) of the piezo-electric field to about 130 kV/cm in ordering direction.

[1]: S. Froyen et al. APL 68, 2852 (1996)

[2]: P. Ernst et al. ICPS 23 World Scientific 1996

[3]: J. D. Perkins et al. JAP, 84 (1998)

Distribution of C-acceptors in delta-doped GaAs studied with Cross-sectional Scanning Tunneling Microscopy

•L. Winking¹, M. Wenderoth¹, T.C.G. Reusch¹, R.G. Ulbrich¹, P.-J. Wilbrandt², R. Kirchheim², S. Malzer³ und G. Döhler^3
1IV. Phys. Inst., Universität Göttingen, Tammannstr.1, D-37077 Göttingen
²Inst. f. Materialphysik, Universität Göttingen, Tammannstr.1, D-37077 Göttingen
³Inst. f. Techn. Physik I, Universität Erlangen-Nürnberg, Erwin-Rommel-Str. 1, D-91058 Erlangen

We present XSTM investigations of the C-acceptor-distribution in delta-doped GaAs. At the intended positions of the C-delta-layers we found at area-densities of 3×10¹²cm^-2 up to extremely high area-densities of 1×10¹⁴cm^-2 a monolayer-sharp spatial distribution of C-acceptors in growth direction. The slight broadening of less than 0.85nm is found to be almost symmetric around the intended position of the delta-layer up to the highest concentration investigated. These results point out that even at the elevated growth temperature of 570^°C and a very high dopant concentration, which was confirmed by SIMS measurements, neither segregation nor coulombic repulsion plays an important role in the system discussed here.

This work was supported by the DFG, SFB 602 TP A7.

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