Evaluation of selective energy contact for hot carrier solar cells based on III–V semiconductors

We investigate hot carrier solar cells using III-V semiconductors. Here, the properties of a quantum well double barrier resonant tunneling structure comprised of Al
_0.6
Ga
_0.4
As/GaAs/Al
_0.6
Ga
_0.4
As was used as selective energy contacts (SEC). The sample was fabricated by MBE on GaAs(001). The GaAs epitaxial layers were used as the optical absorbing layer. A quantum well resonant tunneling structure was adopted here for SEC because of its simplicity and maturity of fabrication technique. Preliminary evaluation was carried out by measuring current-voltage properties under light illumination in order to demonstrate hot carrier generation and collection through SEC. Photocurrent was measured at 77 K and laser excitation was carried out with the emission wavelength of 643 nm and 805 nm which excite the electrons to the conduction band of absorbing layer at ~360 meV and ~10 meV above the band edge, respectively. As a result, a voltage shift toward lower bias voltage was observed in the tail region of tunneling current in photo-assisted current-voltage curve with higher energy excitation compared to that with lower energy excitation. A Monte Carlo simulation taking into account the electron-phonon interaction supports the validity of the measured results. These results indicate generation of hot electrons in the absorbing layer and their extraction through the SEC.