Nanofabrication Technology for Quantum Effect Devices

S. W. Pang, K. K. Ko, and E. W. Berg

University of Michigan, Ann Arbor, Michigan 48109-2122, USA

Low-dimensional quantum confined structures such as quantum dots and quantum wires could provide improved performance for electrical and optoelectronic devices because of the sharp 1-D density of states and the enhanced oscillator strengths. Quantum dots and wires were fabricated by electron beam lithography, dry etching, and epitaxial regrowth. Quantum dots and wires consisted of AlGaAs/InGaAs multiple quantum wells with 25 nm width were generated and etched in a Cl2/Ar plasma. The as-etched quantum dots and wires have smooth surface morphology and vertical profile. Enhanced electro-optic coefficient was observed on waveguides with quantum dots in the active region. Microcavities in In0.20Ga0.80As/GaAs were also fabricated. Significant improvement in the threshold current density has been predicted for microcavity structures in which the width of the optical cavity is reduced to 0.3 µm. 0.25 µm wide microcavities were etched to a depth of 2.8 µm with vertical profile and smooth surface. (Figures 1 and 2)

The in-plane gated (IPG) quantum wire transistor were fabricated using dry etching in a Cl2/Ar plasma generated with the ECR source. The 2DEG in the side gates and the channel are isolated by air gaps, with the 2DEG in the side gates providing electrostatic modulation of the width of the channel. The electric field from the 2DEG in the side gate is parallel to the 2DEG in the channel, resulting in a very efficient coupling of the electric field into the channel. The air gaps between the gates and the channel should provide negligible gate leakage current and small gate capacitance for high frequency operation. Modulation of the 1-D channel width with capacitive coupling using the in-plane gates has been demonstrated, and good device characteristics were obtained. Gate leakage current <0.1 nA was measured on IPG transistors with a gate isolation depth of 520 nm. (Figure 3)

Figure 1. Scanning electron micrograph of quantum dots after dry etching using an ECR source. A Cl2/Ar plasma generated with 50 W microwave power and 50 W rf power at 0.6 mTorr was used.

Figure 2. 0.25 µm wide microcavities in In0.20Ga0.80As/GaAs etched down to 2.8 µm deep.

Figure 3. Scanning electron micrograph of a in-plane gated quantum wire transistor. The in-plane gates were etched by a Cl2/Ar plasma generated with 20% Cl2 using 50 W microwave power and 100 W rf power at 0.5 mTorr.

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Last Updated: November 19, 2007

E-Mail: pang@eecs.umich.edu 

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