Inorganic, Interface-Dominated Heterostructures for Device Concepts
Interface-dominated heterostructure systems like W-type quantum well combinations have enormous application potential in long-wavelength semiconductor lasers. This project aims to develop and optimise such heterostructures and explore their potential as active layers. Building on the experience from the past funding periods, the goal is the demonstration of long-wavelength laser operation beyond the telecom windows. We use the unique materials combination of the two metastable compound semiconductors Ga(N,As) / Ga(As,Bi) to realise a prototypical demonstrator. Both feature relatively low band gap energies due to the incorporation of small fractions of N and Bi, with N acting primarily on the conduction band, Bi primarily on the valence band. The heterostructures with type-II band alignment are grown by metal organic vapour phase epitaxy (MOVPE) using in-situ control with reflectance anisotropy spectroscopy (RAS). Structural characterisation is performed by high-resolution X-ray diffraction (XRD) and atomic force microscopy (AFM) as well as in collaboration with partner projects using transmission electron microscopy.
The relevant hetero band offsets will be tailored by varying alloy composition and strain on the one hand. On the other, the role of doping the layers as Fermi-level control across the internal interface of the heterostructure and, hence, its influence on the band offsets is systematically explored. Moreover, the abruptness of the interface is varied from an abrupt interface to a more spread-out interface inspired by graded-index waveguides. Optical spectroscopy identifies the fundamental transitions, oscillator strength, and band offsets; the latter is corroborated by UV photoelectron spectroscopy. A future device performance is evaluated by transient gain measurements for the various sample design. Optimal structures are processed in bar geometries for gain guided edge emitting lasers allowing for in-operando experiments regarding, e.g., heat dissipation and paving the way for surface emitters.
- T. Hepp, O. Maßmeyer, D.A. Duffy, S.J. Sweeney, K. Volz
Metalorganic vapor phase epitaxy growth and characterization of quaternary (Ga,In)(As,Bi) on GaAs substrates
J. Appl. Phys. 126, 085707 (2019).
- J. Veletas, T. Hepp, K. Volz, S. Chatterjee
Bismuth surface segregation and disorder analysis of quaternary (Ga,In)(As,Bi)/InP alloys
J. Appl. Phys. 126, 135705 (2019).
- P. Kükelhan, T. Hepp, S. Firoozabadi, A. Beyer, K. Volz
Composition determination for quaternary III–V semiconductors by aberration-corrected STEM
Ultramicroscopy 206, 112814 (2019).
Thilo Hepp, Postdoc
Lukas Gümbel, PhD student
Johannes Haust, PhD student
Felix Schäfer, PhD student