Research

Magnetic field enhanced THz generation from semiconductor surfaces

The generation of THz radiation from semiconductor surfaces utilizing the surface depletion/enrichment field is a well established technique and has been examined in detail. THz radiation emitted from semiconductor surfaces can be considerably enhanced applying an external magnetic field. We have performed a systematic study of the power enhancement caused by an external magnetic field for five different semiconductor materials (InSb, InAs, InP, GaAs, GaSb). In particular, we distinguish between the fraction of THz radiation, which was generated by the magnetic field and the surface depletion/enrichment field, respectively. This was possible using time resolved measurements of the THz waveform.

<b>Fig. 1:</b> Typical experimental setup for magnetic field enhanced THz generation from semiconductor surfaces

Using a simple Lorentz model for the acceleration of the carriers with a linear approximation, we have found that the power enhancement caused by the magnetic field is proportional to the square of the applied field for magnetic fields of up to 1 T. The scaling factor for the power enhancement is inversely proportional to the effective electron mass:

The maximum power enhancement factor was obtained for InSb which has the smallest effective electron mass. Because of the small effective electron mass the power enhancement starts to saturate for InSb already at magnetic field strengths of only 0.5 T. The highest absolute power, however, was obtained under any conditions in InAs. This material produces considerably higher THz power even without magnetic field enhancement compared to the other semiconductors InSb, InP, GaSb, and GaAs and no sign of saturation was found for the power enhancement for magnetic fields of up to 1.2 T.

<b>Fig. 2:</b> Enhancement factor for different semiconductor materials

Keywords:

Terahertz (THz), THz generation, semiconductor surfaces, surface emitter, magnetic field enhancement, THz source, time domain spectroscopy (TDS)

References:

[1] "Origin of magnetic field enhancement in the generation of terahertz radiation from semiconductor surfaces", J. Shan, C. Weiss, R. Wallenstein, R. Beigang, and T. F. Heinz, Optics Letters, Vol. 26, No. 11, p. 849-851 (2001)
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[2] "Magnetic field enhanced generation of THz radiation in semiconductor surfaces", C. Weiss, R. Wallenstein, and R. Beigang, Appl. Phys. Lett., Vol. 77, p. 4160 (2000)
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