TY - JOUR
T1 - Surface and interface states of gallium-polar versus nitrogen-polar GaN
T2 - Impact of thin organic semiconductor overlayers
AU - Kim, Hyunjin
AU - Guan, Ze Lei
AU - Sun, Qian
AU - Kahn, Antoine
AU - Han, Jung
AU - Nurmikko, Arto
N1 - Funding Information:
This work was supported by U.S. Department of Energy under Grant No. ER 46387. The work at Yale was partially supported by the U.S. Department of Energy under Contract No. DE-FC26-07NT43227. Work at Princeton was supported by the National Science Foundation (Grant No. DMR-0705920) and the Princeton MRSEC of the National Science Foundation (Grant No. DMR-0819860). FIG. 1. AFM images of (a) Ga-polar and (b) N-polar GaN with the rms roughness of 0.24 nm and 0.48 nm, respectively. LEED patterns for (c) Ga-polar and (d) N-polar GaN with electron beam energy at 138.1 eV and 140.8 eV, respectively. FIG. 2. (a) He I UPS valence band spectra as a function of CuPc coverage on the Ga-polar surface. (The binding energies are referenced to the Fermi level.) (b) Corresponding XPS spectra of the Ga 3 d peak. FIG. 3. (a) He I UPS valence band spectra as a function of CuPc coverage on the N-polar surface. (The binding energies are referenced to the Fermi level.) (b) Corresponding XPS spectra of the Ga 3 d peak FIG. 4. Comparison of XPS Ga 3 d peaks from the as-grown Ga-polar and N-polar GaN surfaces. FIG. 5. Inferred energy band diagrams of as-grown GaN and GaN/CuPc interfaces. (a) As-grown Ga-polar GaN, (b) Ga-polar GaN and CuPc interface, (c) as-grown N-polar GaN, and (d) N-polar GaN and CuPc interface with CuPc thickness of 4 Å (square), 8 Å (diamond), and 20 Å (circle). FIG. 6. (a) I-V characteristic of an InGaN/CuPc device, inset of (a) Schematic of n -(In)GaN/CuPc planar junction structure (typical active area : 0.4 mm 2 ), (b) photocurrent spectrum with 0 V bias and −5 V bias of GaN/CuPc hybrid devices and absorptance of CuPc film. (The intensity of halogen lamp was not normalized), and (c) I-V characteristics at 380 nm under near zero bias at broad range of illumination intensity. FIG. 7. Electron affinity and IE of Ga-polar GaN, N-polar GaN, and CuPc, respectively, inferred from XPS and UPS spectroscopy.
PY - 2010/6/1
Y1 - 2010/6/1
N2 - Using ultraviolet photoemission spectroscopy and x-ray photoemission spectroscopy, we have investigated the electronic properties of interfaces between copper phthalocyanine (CuPc) films and gallium-polar (Ga-polar) and nitrogen-polar (N-polar) GaN surfaces, respectively. Prior to the deposition of CuPc films, the clean Ga-polar and N-polar surfaces exhibited about 0.6 and 0.13 eV upward band bendings, respectively, showing the influence of electronic states on the surface termination and growth direction. With the deposition of ultrathin layers of CuPc, no additional band bending or charge displacement was observed for the Ga-polar heterointerface. In contrast, the N-polar interface exhibited an additional 0.54 eV band bending upon deposition of only a CuPc monolayer, attributed to a partial electron displacement from GaN to CuPc. The difference between the two cases is interpreted in terms of the difference between the electron affinity of the N-polar and Ga-polar GaN surfaces. With potential device use in mind, GaN/CuPc hybrid photodetector devices were fabricated and their photocurrent responses were investigated for possible applications as photosensors.
AB - Using ultraviolet photoemission spectroscopy and x-ray photoemission spectroscopy, we have investigated the electronic properties of interfaces between copper phthalocyanine (CuPc) films and gallium-polar (Ga-polar) and nitrogen-polar (N-polar) GaN surfaces, respectively. Prior to the deposition of CuPc films, the clean Ga-polar and N-polar surfaces exhibited about 0.6 and 0.13 eV upward band bendings, respectively, showing the influence of electronic states on the surface termination and growth direction. With the deposition of ultrathin layers of CuPc, no additional band bending or charge displacement was observed for the Ga-polar heterointerface. In contrast, the N-polar interface exhibited an additional 0.54 eV band bending upon deposition of only a CuPc monolayer, attributed to a partial electron displacement from GaN to CuPc. The difference between the two cases is interpreted in terms of the difference between the electron affinity of the N-polar and Ga-polar GaN surfaces. With potential device use in mind, GaN/CuPc hybrid photodetector devices were fabricated and their photocurrent responses were investigated for possible applications as photosensors.
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U2 - 10.1063/1.3372559
DO - 10.1063/1.3372559
M3 - Article
AN - SCOPUS:77953635197
VL - 107
JO - Journal of Applied Physics
JF - Journal of Applied Physics
SN - 0021-8979
IS - 11
M1 - 113707
ER -