Martin Kamp

Wege in die Nanowelt

Anders als bei den grosen technologischen Revolutionen der Vergangenheit sind es heute eher die kreativen Ideen im Kleinen, die bedeutsame Innovationen vorantreiben. Mit Techniken der Mikrostrukturierung lassen sich Systeme im Mikrometer-Bereich mit vielfaltigen elektronischen, mechanischen, optischen oder fluidischen Funktionen schaffen. In der Nanotechnologie erreicht die Miniaturisierung ihre molekulare und atomare Grenze. Wahrend Mikrosysteme noch analog zu geeignet verkleinerten klassischen Makrosystemen arbeiten, kommt es auf der Nanometer-Skala vor allem aufgrund quantenmechanischer Effekte zu neuen Eigenschaften, die nunmehr technologisch erschlossen werden.

Nanolasers operating in the regime of strong coupling (Conference Presentation)

The development and physical understanding of high-beta nanolasers operating in regime of cavity-quantum-electrodynamics (cQED) is a highly interdisciplinary field of research, involving important aspects of nanotechnology, quantum optics, and semiconductor physics. Of particular interest is the quantum limit of operation, in which a few or even a single emitter act as gain material.nnThe regime of strong light-matter coupling is typically associated with weak excitation. With current realizations of cQED systems, strong coupling may persevere even at elevated excitation levels sufficient to cross the threshold to lasing. In the presence of stimulated emission, the vacuum-Rabi doublet in the emission spectrum is modified and the established criterion for strong coupling no longer applies.nnBased on an analytic approach, we provide a generalized criterion for strong coupling and the corresponding emission spectrum that includes the influence of higher Jaynes-Cummings states. The applicability is demonstrated in a theory-experiment comparison of a state-of-the-art few-emitter quantum-dot (QD)–micropillar laser as a particular realization of the driven dissipative Jaynes-Cummings model [1]. Furthermore, we address the question if and for which parameters true single-emitter lasing can be achieved. By using a master-equation approach for up to 8 QDs coupled to the mode, we provide evidence for the coexistence of strong coupling and lasing in our system in the presence of background emitter contributions by identifying signatures in the mean-photon number, the photon-autocorrelation function, and the emission linewidth.nn[1] C. Gies et al., accepted for publication in PRA, arxiv:1606.05591

Mid-infrared detectors based on resonant tunneling diodes and interband cascade structures

Molecule and gas sensing is a key technology that is applied in multiple environmental, industrial and medical fields. In particular optical detection technologies enable contactless, nondestructive, highly sensitive and fast detection of even smallest concentrations of trace gases and molecules. During the past years, an increasing demand for mid-infrared (MIR) light sources suitable for, e.g. molecule or gas sensing applications, has driven the development and optimization of novel MIR lasers and light sources, such as quantum cascade lasers (QCL) or interband cascade lasers (ICL). Despite the progress on MIR light sources, there is still a lack in appropriate MIR detectors. Here, we present and discuss two promising and novel GaSb/InAs-based detector concepts. First, resonant tunneling diode (RTD) photodetectors as an alternative to avalanche photodetectors. In RTDs, amplification of photogenerated minority charge carriers is based on modulation of a majority charge carrier resonant tunneling current. Second, interband cascade photodetectors (ICD), in which a cascading scheme allows for fast carrier extraction and a compensation of the diffusion length limitation.

Antimonide-based resonant tunneling photodetectors for mid infrared wavelength light detection

We present antimonide-based resonant tunneling photodetectors with GaSb/AlAsSb double barrier structures and pseudomorphically grown prewell emitter structures comprising the ternary compound semiconductors GaInSb and GaAsSb. Due to the incorporation of GaInSb and GaAsSb prewell emitters, room temperature resonant tunneling with peak-to-valley current ratios of up to 2.4 are shown. The room temperature operation is attributed to the enhanced Γ-Lvalley energy separation and consequently a re-population of the Γ-conduction band of the ternary compound emitter prewell with respect to bulk GaSb. By integration of a quaternary absorption layer, RTDs photodetectors with cut-off wavelengths up to 3 μm have been realized.

Mid infrared DFB interband cascade lasers

The mid infrared spectral range (MIR) is of great interest for a variety of industrial, medical and environmental applications since numerous molecules have strong absorption lines therein. Interband cascade lasers (ICLs) have the ability to cover the entire MIR almost independently from the bandgap of the utilized semiconductors. Combined with a DFB technology which is applicable for most kinds of interband transition based semiconductor lasers the spectral range between 2.8 and 5.9 μm could be covered with application grade single mode devices with low power consumption. Recent optimizations regarding the layer design as well as the device processing yielded DFB laser chips with improved performance that will pave the way for a variety of applications that benefit from reasonable output power.

Interband Cascade Laser Based Sensing

Recent progress on Interband Cascade Lasers for gas sensing in the mid-infrared will be discussed. Improvements in epitaxial design and DFB laser device processing along with high-impact industrial applications of the lasers will presented.

Two Photon Interference from Semiconductor Quantum Dots

We study the interference properties of single photons emitted from semiconductor quantum dots (QDs). The influence of the excitation conditions, as well as the nature of the QD-source (same dot or separate dots) is assessed, and we provide a consistent model to describe the data quantitatively.

Free Space Quantum Key Distribution over 500 Meters using Electrically Triggered Quantum Dot Single-Photon Sources

Summary form only given. The field of quantum key distribution has made rapid advances in the past years. Networks of QKD links were implemented, commercial QKD systems are available and research systems have reached GHz repetition rates and distances beyond 200 km. Usually decoy protocols with attenuated laser light pulses are used, where the asymptotic key rate of a QKD system is proportional to the fraction of single photon pulses sent [1]. Single photon sources (SPSs) intrinsically have a higher single photon fraction and thus reach higher key rates.

Bright quantum dot single photon source based on a low Q defect cavity

The quasi-planar single photon source presented in this paper shows an extraction efficiency of 42% without complex photonic resonator geometries or lithography steps as well as a high purity with a g2(0) value of 0.023.