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A photocontrolled InGaAs/AlAs double‐barrier resonant‐tunneling diode, for the first time, has been demonstrated. The photoinduced valley current in the resonant‐tunneling diode was optically controlled by varying the incident optical power level. With the incident optical power intense enough, the photogenerated valley current became dominant over the peak current. As a consequence, the negative differential resistance of the device was nullified. A photogeneration process, based on photogenerating carriers in the depletion region adjacent to the double barriers, is described and characterized. The device under illumination was modeled as a resonant‐tunneling diode in series integration with a photodetector. The quantum efficiency for the photogeneration was measured and found comparable with theoretical prediction. The demonstrated photocontrolled double‐barrier resonant‐tunneling diode can be useful in a variety of applications.

Intersubband transitions from the ground state to the first and second excited states in pseudomorphic AlGaAs/InGaAs/GaAs/AlGaAs multiple step quantum wells have been observed. The step well structure has a configuration of two AlGaAs barriers confining an InGaAs/GaAs step. Multiple step wells were grown on GaAs substrate with each InGaAs layer compressively strained. During the growth, a uniform growth condition was adopted so that inconvenient long growth interruptions and fast temperature ramps when switching the materials were eliminated. The sample was examined by cross‐sectional transmission electron microscopy, an x‐ray rocking curve technique, and the results show good crystal quality using this simple growth method. Theoretical calculations were performed to fit the intersubband absorption spectrum. The calculated energies are in good agreement with the observed peak positions for both the 1→2 and 1→3 transitions.

Normal incidence electron intersubband transition in InGaAs/GaAs square quantum wells has been observed. With the incident light polarized (x axis) perpendicular to the growth direction (z axis) of the quantum well, a distinct absorption peak was observed. The absorption peak occurs at a different frequency from the peak induced by a mixed yz‐polarized light. The latter has a smaller peak strength and is shifted at a lower frequency in the absorption spectrum, and the shift can be interpreted in part as a result of the depolarization effect. The mechanism responsible for the observation of the normal incidence absorption is discussed.