GaBiAs layers for terahertz optoelectronic devices activated by 1 μm wavelength laser pulses

Vaidas Pačebutas ,  Andrius Bičiūnas ,  Klemensas Bertulis ,  Arūnas Krotkus 

Semiconductor Physics Institute, A.Gostauto 11, Vilnius LT-01108, Lithuania

Abstract

Majority of pulsed THz systems are presently using Ti:sapphire lasers emitting at the wavelengths around 800 nm and photoconductive components made from low-temperature-grown GaAs (LTG GaAs) epitaxial layers. Ti: sapphire lasers are quite bulky and complicated, thus using of compact, efficient, and cost-effective solid-state and fiber laser systems that are directly pumped by diode-laser bars and are generating femtosecond pulses at wavelengths of 1 μm and 1.5 μm would be advantageous for THz applications.

In this contribution we will present the research on technology and physical characteristics of a novel semiconductor compound – LTG GaBiAs. The energy bandgap of this ternary compound can be shifted to narrower values by adding Bi much faster than, e.g., the bandgap of InGaAs when Ga-atoms are exchanged by In-atoms. Moreover, electron trapping times in GaBiAs shorter than ~0.5 ps can be easily achieved during the low-temperature growth of this material.

Epitaxial GaBixAs1-x layers were grown on semi-insulating (100)-oriented GaAs substrates in a solid-state molecular-beam-epitaxy (MBE) system at substrate temperatures ranging from 240 to 350o C; the Bi-content in the layers growth at the lowest temperatures has reached x=0.11, which has corresponded to the energy bandgap of the alloy of 0.9 eV. The majority of the investigations were performed on the layers with x=0.08 that were sensitive to the radiation of femtosecond Yb:KGW laser (the wavelength of 1030 nm) used in the experiments of THz radiation emission and detection.

As-grown GaBixAs1-x layers were of a p-type conduction with dark resistivity exceeding 1000 Ωcm. Electron mobility in the layers as measured by using the optical pump – THz probe technique was larger than 2000 cm2/Vs. The same technique was employed also for the determination of the electron lifetimes, which, depending on the growth conditions, ranged from several picoseconds to less than 1 ps. All these material parameters satisfy the requirements that are set when manufacturing photoconductive switches used for optoelectronic THz radiation emission and detection.

Both THz emitters and THz detectors were made from GaBixAs1-x layers. When activated by 70-fs duration Yb:KGW laser pulses the system has produced THz transients with a bandwidth reaching 5 THz and signal-to-noise ratio of 60 dB.

 

Presentation: Oral at E-MRS Fall Meeting 2009, Symposium D, by Vaidas Pačebutas
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-11 11:09
Revised:   2009-08-13 17:30