We present unambiguous experimental evidence for the dramatic dependence of hole tunneling rates on in-plane momentum in (Ga,In)As/(Al,In)As asymmetric double quantum wells. Holes generated near the band edge tunnel on hundred picosecond time scales, whereas holes excited with large excess energy tunnel on subpicosecond time scales. The mechanism responsible for this increase of more than three orders of magnitude in the hole tunneling rate is nonresonant delocalization of hole wave functions by band mixing in the valence band.
A high contrast, low intensity GaAlInAs/AlInAs multiple quantum well asymmetric Fabry–Perot reflection modulator for operation at 1.3 μm has been demonstrated. The reflection modulator takes advantage of the large absorptive and refractive nonlinearities associated with saturating the heavy-hole exciton resonance. We achieve an on/off contrast ratio in excess of 1000:1 (30 dB) and an insertion loss of 2.2 dB at a pump intensity of 30 kW/cm2, corresponding to a carrier density of 4.5×1017 cm−3. The modulator was demonstrated to have a large operating bandwidth, achieving an on/off contrast ratio of greater than 100:1 over a 5 nm optical band. The operating speed of the modulator was measured and found to approach 1 GHz.
We report enhanced electroabsorption in selectively doped (Ga,In)As/(Al,In)As asymmetric double quantum wells (ADQWs) by the use of real space electron transfer. The electron concentration in both the wide and narrow wells is investigated by field dependent absorption and photoluminescence spectroscopy. The results are compared to absorption changes in an undoped ADQW structure that utilizes the quantum confined stark effect. The doped modulator exhibits a significantly larger red shift with applied field than the undoped structure.
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