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(Color online) (A) Schematic of an n-i-n-doped InP NW. (B) SE image of a native oxide covered NW showing a bright undoped segment (hν = 70 eV, kinetic energy (KE) = 0.9 eV). (C) XPEEM image using electrons from the In 4d core level of the NW (hν = 70 eV, KE = 47.3 eV). (D) Mirror mode image of an uncleaned NW. (E) Schematic energy band diagram showing the SE emission process as described in Ref. 15. The ionization energies for the two segments are equal (En = Ei ), and the vacuum level potential (Evac ) is non-uniform outside the sample. Thus, electrons from the n-type part need ΔEn more energy to reach the detector energy level (EDetector ). Ec , Ev , and EF denote the conduction band edge, valence band edge, and Fermi level, respectively. The false color code in (B, C) depicts the photoelectron intensity with increasing intensity: black-green-yellow-red in the online figure (intrinsic segment in (B) is brightest).
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(Color online) (A) SE image of a cleaned InP n-i-n-NW (hν = 133 eV, KE 0 eV). (B) Intensity profile along the marked line in (A). The dotted lines mark the two space charge regions (SCRs): The left SCR is 300 nm wide and the right SCR is 200 nm. The Au-particle can be found at the far right in the image.
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InPnanowires (NWs) with differently doped segments were studied with nanoscale resolution using synchrotron based photoemission electron microscopy. We clearly resolved axially stacked n-type and undoped segments of the NWs without the need of additional processing or contacting. The lengths and relative doping levels of different NW segments as well as space charge regions were determined indicating memory effects of sulfur during growth. The surface chemistry of the nanowires was monitored simultaneously, showing that in the present case, the doping contrast was independent of the presence or absence of a native oxide.
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