Ballistic Electron Emission Luminescence of InAs Quantum Dots Embedded in a GaAs/Al x Ga 1-x As Heterostructure
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Ballistic Electron Emission Luminescence of InAs Quantum Dots Embedded in a GaAs/AlxGa1-xAs Heterostructure Wei Yi, Ian Appelbaum, Kasey J. Russell, and Venkatesh Narayanamurti Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, U.S.A. Micah P. Hanson and Arthur C. Gossard Materials Department, University of California, Santa Barbara, CA 93106, U.S.A. ABSTRACT Ballistic electron emission luminescence (BEEL) is a further development of ballistic electron emission microscopy (BEEM) combining three-terminal hot electron injection and interband radiative recombination in direct-gap semiconductor materials. By using a planar tunnel-junction emitter rather than a STM tip, a spectrographic analysis of the induced electroluminescence can be performed with the help of much higher current injection level. We demonstrate the operational principle of BEEL in a GaAs/AlxGa1-xAs heterostructure with a layer of InAs quantum dots (QDs) as the optical active layer. The wavelength-resolved BEEL spectra from planar tunnel-junction devices disclose the QD luminescence as a peak near 1.34 eV accompanied with a linear quantum-confined Stark shift. At higher collector voltage, luminescence from bulk states of GaAs peaked at 1.48 eV is observed. The spectrally integrated BEEL intensity as a function of collector voltage fits well with the results from STM tip injection, which is measured in a single-photon-counting mode. Measurement of ballistic electron current spectroscopy is made possible by freezing out the thermionic leakage current at low temperatures. Our results indicate that it is feasible to simultaneously acquire topographic, electronic and photonic information of buried light-emitting semiconductor heterostructures.
INTRODUCTION Ballistic electron emission microscopy (BEEM) is a three-terminal variation of a scanning tunneling microscope (STM) in the configuration of a hot electron transistor. By using a tunneling tip instead of a solid-state tunnel junction (TJ), hot electrons are injected ballistically through the thin metal base layer over the Schottky barrier at the metal-semiconductor interface into the semiconductor collector. Initially used as a local probe of the Schottky barrier heights (SBHs) at metal-semiconductor interfaces, BEEM has also been applied to study local transport properties such as bandoffsets, resonant tunneling, and carrier confinement through semiconductor heterostructures including quantum wells, superlattices, and quantum dots, provided that the structures of interest are buried within the range of ballistic mean free path. BEEM has been shown to be a powerful nondestructive tool for local characterization of the structural and electronic properties of semiconductor materials with nanometer spatial resolution and meV energy resolution [1, 2]. Combining BEEM with a luminescence technique would give valuable information about local current transport and light-emission properties of direct-gap semiconductor heterostructures that have important optoelectronic
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