Abstract:We identified p-type nanoscale dopant-induced dots that are formed by fluctuations of the dopant atom distribution in sufficiently thin GaAs p-n multilayers. Their electronic structure and the resulting potential variations were investigated by cross-sectional scanning tunneling microscopy and spectroscopy as a function of the number of dopant atoms within the dot. We find significant changes in the current-voltage characteristics of the dots compared to spatially nonconfined material, due to a reduced ability… Show more
“…The number of screening electrons at the surface depends then on the conduction-band density of states and not on the doping concentration, in analogy to the hole accumulation in the valence band described for differently p-doped GaAs͑110͒ in Ref. 17. The different screening origin can also be recognized in the depth dependence of the band bending shown in the inset of Fig.…”
Section: Theoretical Background and Details Of The Calculationmentioning
We investigated the origins of the tunnel current in scanning tunneling microscopy ͑STM͒ and spectroscopy experiments on GaN͑1100͒ surfaces. By calculating the tunnel currents in the presence of a tip-induced band bending for unpinned n-type GaN͑1100͒ surfaces, we demonstrate that only conduction-band states are observed at positive and negative voltage polarities independent of the doping concentration. Valence-band states remain undetectable because tunneling out of the electron-accumulation zone in conduction-band states dominates by four orders of magnitude. As a result band-gap sizes cannot be determined by STM on unpinned GaN͑1100͒ surfaces. Appropriate band-edge positions and gap sizes can be determined on pinned surfaces.
“…The number of screening electrons at the surface depends then on the conduction-band density of states and not on the doping concentration, in analogy to the hole accumulation in the valence band described for differently p-doped GaAs͑110͒ in Ref. 17. The different screening origin can also be recognized in the depth dependence of the band bending shown in the inset of Fig.…”
Section: Theoretical Background and Details Of The Calculationmentioning
We investigated the origins of the tunnel current in scanning tunneling microscopy ͑STM͒ and spectroscopy experiments on GaN͑1100͒ surfaces. By calculating the tunnel currents in the presence of a tip-induced band bending for unpinned n-type GaN͑1100͒ surfaces, we demonstrate that only conduction-band states are observed at positive and negative voltage polarities independent of the doping concentration. Valence-band states remain undetectable because tunneling out of the electron-accumulation zone in conduction-band states dominates by four orders of magnitude. As a result band-gap sizes cannot be determined by STM on unpinned GaN͑1100͒ surfaces. Appropriate band-edge positions and gap sizes can be determined on pinned surfaces.
“…The short range fluctuations are due to single dopant atoms or surface impurities and introduce only faint distortions of the uniform potential drop. The long range fluctuations are visible by the slight bending of the contour lines and might originate from dopant clustering effects as previously observed in p-n superlattices [97]. Besides these slight distortions the built-in potential drops very uniformly across the p-i-n interface.…”
Section: The P-i-n Diode As Source For An Adjustable Electric Field 54mentioning
“…1͒. Schottky barrier inhomogeneities, 9 which have been observed at nonepitaxial interfaces, [10][11][12][13] do not play a role here, as they are due to variations in the atomic arrangement at the metal-semiconductor interface itself. The metal-semiconductor interfaces in our devices are perfectly epitaxial and monocrystalline, which is supported by crosssectional transmission electron micrographs of similar structures.…”
Section: A Room-temperature Measurementsmentioning
We show that individual dopant atoms dominate the transport characteristics of nanometer-sized devices, by investigating metal-semiconductor diodes down to 15 nm diameter. Room-temperature measurements reveal a strongly increasing scatter in the device-to-device conductance towards smaller device sizes. The lowtemperature measurements exhibit pronounced features, caused by resonant tunneling through electronic states of individual dopant atoms. We demonstrate by a statistical analysis that this behavior can be explained by the presence of randomly distributed individual dopant atoms in the space-charge region.
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