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Iron doped InGaAs: Competitive THz emitters and detectors fabricated from the same photoconductor

: Globisch, B.; Dietz, R.J.B.; Kohlhaas, R.B.; Göbel, T.; Schell, M.; Alcer, D.; Semtsiv, M.; Masselink, W.T.


Journal of applied physics 121 (2017), No.5, Art. 053102, 13 pp.
ISSN: 0021-8979
ISSN: 1089-7550
Deutsche Forschungsgemeinschaft DFG
GO 2533/2-1
Journal Article
Fraunhofer HHI ()

Today, the optimum material systems for photoconductive emitters and receivers are different. In THz reflection measurements, this leads to complicated optics or performance compromises. We present photoconductive emitters and detectors fabricated from molecular beam epitaxy (MBE) grown iron (Fe) doped InGaAs, which are well suited for a THz time-domain spectroscopy as both emitters and detectors. As a photoconductive emitter, 75 mu W +/- 5 mu W of radiated THz power was measured. As a detector, THz pulses with a bandwidth of up to 6 THz and a peak dynamic range of 95 dB could be detected. These results are comparable to state-of-the-art THz photoconductors, which allows for simple reflection measurements without a performance decrease. The incorporation of Fe in InGaAs during MBE growth is investigated by secondary ion mass spectroscopy, Hall, and transient differential transmission measurements. Growth temperatures close to 400 degrees C allow for homogeneous Fe doping concentrations up to 5 x 10(20) cm(-3) and result in a photoconductor with an electron lifetime of 0.3 ps, a resistivity of 2 k Omega cm, and an electron mobility higher than 900 cm(2) V-1 s(-1). We show that iron dopants are incorporated up to a maximum concentration of 1 x 10(17) cm(-3) into substitutional lattice sites. The remaining dopants are electrically inactive and form defects that are anneal-stable up to a temperature of 600 degrees C. The fast recombination center in Fe-doped InGaAs is an unidentified defect, representing approximate to 0.5% of the nominal iron concentration. The electron and hole capture cross section of this defect is determined as sigma(e) = 3.8 x 10(-14) cm(2) and sigma(h) = 5.5 x 10(-15) cm(2), respectively.