Surface Built-in Electric Field Research Articles

Electron distribution and electrical properties of InAs quantum wells

We have investigated the dependence of the electrical characteristics on the vertical electric fields in InAs/(Al x Ga 1- x )Sb double heterostructures by Hall effect measurements. By measuring the samples with different upper barrier thicknesses, we have observed the mobility modulation in the (AlGa)Sb/InAs/AlSb heterostructures by effectively changing the surface electric field. The mobility modulation is attributed to the modulated scattering probability depending on the electron distribution in the quantum well due to the built-in surface electric field. The proportionality coefficient of the sheet carrier concentration against inverse upper barrier thickness roughly corresponds to the potential difference between the Fermi energy in the InAs quantum well and the surface pinning level of GaSb under flat-band conditions.

Photomodulation Spectroscopy in GaSe

Photoabsorption and photoreflectance spectra have been measured in a semiconducting layer-compound GaSe in the exciton energy region at temperatures between ∼300K and ∼80K. The photomodulation at the frequency of 10Hz∼200kHz has been found to be useful as the means of thermomodulation without a contact. A high-frequency photoabsorption experiment at the modulatiorn frequency of 5 MHz has also been performed using a pair of picosecond dye lasers. In this experiment, time behavior of the photomodulation signal has been determined from the dependence of the signal intensity on the delay time of the probe pulse and also on the phase of the lock-in amplifier. The dominant modulation mechanisms of this experiment have been identified as the spectral variation due to the reduction of the built-in surface electric field and the exciton-exciton collision.