G. Dehlinger

Intersubband absorption performed on p-type modulation-doped Si0.2Ge0.8/Si quantum wells grown on Si0.5Ge0.5 pseudosubstrate

We present intersubband absorption measurements performed on p-type quasistrain-compensated modulation-doped Si0.2Ge0.8/Si quantum wells grown on Si0.5Ge0.5 pseudosubstrates. Several intersubband absorption peaks are observed up to room temperature. A strong confinement shift of the resonance occuring between the ground and the first excited heavy hole states has been observed, with the absorption peak shifting from λ=5.3u2009μm to as short as 3.8 μm. Excellent overall agreement with a 6 band k⋅p calculation is obtained, proving the accuracy of recently predicted values of band offsets.

Analysis of the Metallic Phase of Two-Dimensional Holes in SiGe in Terms of Temperature Dependent Screening

We find that temperature dependent screening can quantitatively explain the metallic behavior of the resistivity on the metallic side of the so-called metal-insulator transition in p-SiGe. Interference and interaction effects exhibit the usual insulating behavior which is expected to overpower the metallic background at sufficiently low temperatures. We find empirically that the concept of a Fermi liquid describes our system with its large interaction parameter r(s) approximately 8.

Single-hole transistor in a p-Si/SiGe quantum well

A single-hole transistor is patterned in a p-Si/SiGe quantum well by applying voltages to nanostructured top gate electrodes. Gating is achieved by oxidizing the etched semiconductor surface and the mesa walls before evaporation of the top gates. Pronounced Coulomb blockade effects are observed at small coupling of the transistor island to source and drain.

Coexistence of weak localization and a metallic phase in Si/SiGe quantum wells

Magnetoresistivity measurements on p-type Si/SiGe quantum wells reveal the coexistence of a metallic behavior and weak localization. Deep in the metallic regime, pronounced weak localization reduces the metallic behavior around zero magnetic field without destroying it. In the insulating phase, a positive magnetoresistivity emerges close to B=0, possibly related to spin-orbit interactions.

Valence band intersubband electroluminescence from Si/SiGe quantum cascade structures

Abstract The principle of intersubband emission is applied to the Si/SiGe material system, using hole intersubband transitions in structures grown pseudo-morphically on Si substrate by molecular beam epitaxy. Cascade structures consisting of three times four repetitions of a five quantum well sequence are investigated. The design constraints are found to be imposed mainly by the total amount of strain, giving limitations to the number of wells per cascade and the total number of cascade periods. Despite the close approach to the critical thickness for misfit dislocations, requiring low temperature growth, these structures reveal intersubband electro-luminescence with a linewidth as narrow as 22meV. Peak energies between 125 and 154meV are obtained by tuning the well width and Ge content of the single active quantum well. By comparison with the emission from a III–V cascade structure, the non-radiative lifetime of the upper emission state is determined. It is found to depend strongly on the structures design, but can reach values comparable to those in similar III–V cascade structures. A discussion of the importance of carrier escape to the continuum and the injection efficiency, as well as the relaxation via the light hole state is given.

Voltage-tunable, two-band mid-infrared detection based on Si/SiGe quantum-cascade injector structures

Photocurrent spectroscopy has been performed on doped Si/SiGe valence band cascade injector structures in the mid-infrared spectral region. A large tunability of the photoresponse peak wavelength (from 5.2 to 3.2 μm) by an externally applied electric field is observed. The tunability of the photoresponse is a consequence of an electric-field-induced transfer of holes from the deepest to the shallowest quantum well of the injector sequence. Depending on the bias voltage, dark-current-limited peak detectivities of D*=1×109u2009cmHz/W (peak wavelength 5 μm at −4u2009V bias) and of D*=1.3×109u2009cmHz/W (peak wavelength 3.2 μm at 5 V bias) are obtained at a temperature of 77 K.

Analysis of the resistance of two-dimensional holes in SiGe over a wide temperature range

The temperature dependence of a system exhibiting a ‘metal–insulator transition in two dimensions at zero magnetic 2eld’ (MIT) is studied up to 90 K. Using a classical scattering model we are able to simulate the non-monotonic temperature dependence of the resistivity in the metallic high density regime. We show that the temperature dependence arises from a complex interplay of metallic andinsulating contributions containedin the calculation of the scattering rate 1 =� D(E; T ), each dominating in a limited temperature range. ? 2002 Elsevier Science B.V. All rights reserved.

Investigation of the emitter structure in SiGe/Si resonant tunneling structures

Pseudomorphically grown p-type Si/SiGe double barrier resonant tunneling diodes have been investigated. The main resonances are shown to be due to tunneling through heavy and light hole states in the well. However, temperature activated resonances and resonances arising in a B-field perpendicular to the current show the importance of the complicated emitter structure and its energy spectrum.

Intersubband quantum cascades in the Si/SiGe material system

AbstractSi=SiGe quantum cascade structure of 3 × 4 periods show well-resolved intersubband electroluminescence, whose non-radiativelifetimesarefoundtodependstronglyonthedesignofthequantumwellstructure,andareshowntoreachvaluescomparabletothatofanequivalentGaInAs=AlInAslaserstructure.ProblemsthatneedtobeovercomefortherealizationofaSi=SiGequantumcascadelaserarediscussedinrelationtostructuresonrelaxedSiGebuerlayers.InitialexperimentsusingSi 0:2 Ge 0:8 =SionSi 0:5 Ge 0:5 buerlayersshowwell-resolvedintersubbandabsorptionbetweentwoheavyholestatesinthequantumwells.? 2002ElsevierScienceB.V.Allrightsreserved. Keywords:Intersubband; Quantumcascade;SiGe 1. IntroductionThequantumcascade(QC)laserisrapidlyadvan-cing as a viable option for mid-IR emission, cover-ing today a large wavelength range, 3–24 m. Withan improved understanding of the intersubband pro-cesses, it has been possible to extend the operationtocontinuousmodeandroomtemperatureoperation[1]. The conception of a laser working through in-tersubbandtransitionshasalsospurredaninterestforapplyingthesameideastoSi-basedheterostructures,whoseindirectbandgapisalargeimpedimenttoe-cientinterbandlightemissionandlasing.Incontrast,forintersubbandemissionthenatureofthebandgapisinconsequential.ThemotivationforaSi-QClaseristwofold.WithSiMOSFETtechnologydominating

Si/SiGe quantum cascade structures emitting in the 10 μm range

Abstract In this paper, we report on the successful deposition of Si/SiGe quantum cascade (QC) structures by molecular beam epitaxy (MBE). The structures are pseudomorphically grown on Si in the metastable regime, thus low temperature (T=350xa0°C) deposition is required. Structural characterization has been performed using transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray reflectivity (XRR). The data indicate an interface roughness of about 2 monolayers and an excellent correlation of the layer periodicity within the stacks of cascades. Electroluminescence (EL) has been observed for several different p-type Si/SiGe QC structures. The observed energy agrees with the energy calculated for the HH2 to HH1 intersubband transition in the active well of the cascade structure and shows the expected confinement shift in dependence of the Ge concentration and the well width. The EL is strongly p-polarized. The results clearly indicate that the observed EL originates from the desired intersubband transition. The EL persists up to temperatures exceeding 180 K. The non-radiative lifetime of the HH2 state reaches values of about 0.5 ps, which is comparable to those of III/V QC structures.