Differential Absorption Spectroscopy of Charge Distributions in Double-Barrier Tunnel Structures.

Differential Absorption Spectroscopy is used to determine the charge density in InGaAs/InAlAs double-barrier tunneling structures. We show the formation of accumulation and depletion regions on either side of the double barrier, and measure the accumulated charge in the 45angstroms quantum well region of the structures. Peak charge densities ~5.4x10 sup (10) cm sup (-2) and ~3. 9x10 sup (10) cm sup (-2) are measured for barrier thickness 70angstroms and 56angstroms, respectively. The corresponding calculated transit times are 70ps and 20ps, in an agreement with the coherent tunneling model.