Olaf Weidemann

 
Year:

Research


AlN on diamond

AlN and diamond both feature the advantages of wide band gap materials for high power and optoelectronic devices. In addition, diamond has a superior thermal conductivity which can handle increasing power densities in modern devices. However, the lack of efficient p-type doping of AlN and n-type doping of diamond so far does not allow the fabrication of efficient bipolar devices from either material. This drawback can be overcome by combining n-type AlN and p-type diamond in a heterostructure device, which in turn requires an in depth understanding of the structural and electrical properties of the diamond/AlN interface.
Important parameters are the offsets in valence and conduction band as well as the band bending due to interface charges (Fig. 1). We use an in-situ photoelectron spectroscopy system directly attached to a group III-nitride molecular beam epitaxy (MBE) system to determine band offsets and band bending at the AlN/diamond interface.

 


Figure 1: Band scheme at a heterojunction showing band offsets and bending


GaN quantum dots in AlN matrix

Quantum dots (QDs) are of special interest for both fundamental physics and optoelectronic applications. On the other hand, GaN-based devices have been shown useful to detect chemically induced changes of the surface potential, thereby acting as chemical sensors in liquid or gaseous environments. Chemical sensors with new functionalities can be realized by using GaN QDs as optical probes for the detection of variations in the surface potential.
To achieve this, a detailed understanding of the QD optical properties and its dependence on variation in an externally applied electric field is necessary. The QD are studied by means of photoluminescence (PL) measurements over a temperature range of 4K to 200°C. 3D simulation with nextnano3 are used to interpret the electric field dependence of the PL spectra for various dot sizes, stack number or spacer thicknesses.


Figure 2: nextnano3 software simulations of electron (green) and hole (blue) wavefunctions

When equipped with a catalytic, semitransparent top Pt gate, the QDs can be used as a hydrogen sensor. The hydrogen dissociates at the Pt gate and diffuses to the Pt/AlN interface, where it forms an electric dipole layer. This modifies the electric field inside the dot layers and changes the measured PL intensity. This work supported by the European project DOTSENSE.

 

Publications

GaN quantum dots as optical transducers for chemical sensors

Applied Physics Letters 94, 113108 (2009)

O. Weidemann | P. K. Kandaswamy | E. Monroy | G. Jegert | M. Stutzmann | M. Eickhoff

Online Reference

Gas Sensing Interactions at Hydrogenated Diamond Surfaces

Sensors Journal, IEEE 7 9 1349-1353 (2007)

A. Helwig | G. Müller | O. Weidemann | A. Haertl | J. A. Garrido | M. Eickhoff

Online Reference

Modulation spectroscopy of AlGaN/GaN heterostructures: The influence of electron-hole interaction

physica status solidi (a) 204 2 447-458 (2007)

R. Goldhahn | A. T. Winzer | A. Dadgar | A. Krost | O. Weidemann | M. Eickhoff

Online Reference

Electroreflectance spectroscopy of Pt/AlGaN/GaN heterostructures exposed to gaseous hydrogen

APPLIED PHYSICS LETTERS 88 2 024101 (2006)

A. T. Winzer | R. Goldhahn | G. Gobsch | A. Dadgar | A. Krost | O. Weidemann | M. Stutzmann | M. Eickhoff

Online Reference

Influence of thermal oxidation on the electronic properties of Pt Schottky contacts on GaN grown by molecular-beam epitaxy

APPLIED PHYSICS LETTERS 86 8 083507 (2005)

O. Weidemann | E. Monroy | E. Hahn | M. Stutzmann | M. Eickhoff

Online Reference

Electronics and sensors based on pyroelectric AlGaN/GaN heterostructures

phys. stat. sol. (c) 0, 1908-1918 (2003) (review article)

M. Eickhoff | J. Schalwig | G. Steinhoff | O. Weidemann | L. Görgens | R. Neuberger | M. Hermann | B. Baur | G. Müller | O. Ambacher | M. Stutzmann

Online Reference

Influence of surface oxides on hydrogen-sensitive Pd : GaN Schottky diodes

APPLIED PHYSICS LETTERS 83 4 773-775 (2003)

O. Weidemann | M. Hermann | G. Steinhoff | H. Wingbrant | A. L. Spetz | M. Stutzmann | M. Eickhoff

Online Reference

TUM Technische Universität München TUM Technische Universität München Physik Department Elektrotechnik und Informationstechnik TUM Technische Universität München
 

Events & News

17 Jan 2018

ERC Consolidator Grant for Gregor Koblmüller   more

10 Aug 2017

Best Poster Awards for Ganpath Veerabathran and Alexander Andrejew at iNOW 2017   more

27 Jun 2017

Best Poster Award at Nanowire Week for Jochen Bissinger   more

15 Mar 2017

Dr. Kai Müller admitted to the “Junges Kolleg” of the Bavarian Academy of Sciences   more

27 Feb 2017

Two-photon pulses from a single two-level system   more

Seminars

January 26, 2018

Reliability of hexagonal boron nitride dielectric stacks for CMOS applications   more

January 23, 2018

Helical states, spin-orbit coupling, and phase-coherent transport in InAs nanowires   more

January 16, 2018

New insights into novel (and conventional) materials using polarization-sensitive infrared magneto-spectroscopy   more