Abstract

In the last few years many efforts have been made to investigate impulsively excited plasma oscillations in semiconductors. In this paper we present the first measurements of optically excited intrasubband plasmons in modulation-doped single quantum wells. The sample is excited under an incident angle of 45° with 100-fs pulses from a Thsapphire laser operating at a photon energy of 1.596 eV. Radiative plasmon modes emit THz pulses via a 3-μm grating coupler on top of the sample. The emitted THz radiation is collected by two paraboloidal mirrors and detected with an ion-implanted silicon-on-sapphire antenna, which is gated with a time-delayed second part of the laser beam. The molecular beam epitaxy (MBE)-grown sample consists of a single 17-nm-thick GaAs well, which is embedded into 80-nm (bottom) and 2-nm (top)-thick Al-GaAs spacer layers. Modulation doping is achieved by two Si-doped AlGaAs layers forming a two-dimensional electron gas (2DEG) inside the well. The electron density and the low field mobility of the sample is 9.0 × 10¹¹ cm⁻² and 2.6 × 10⁵ cm²/Vs (at 4.2 K), respectively. At low temperatures only the lowest subband is occupied with the cold plasma electrons. The measurements are performed at 8 K.

© 1998 Optical Society of America