Valence-band ordering in ZnO

Reynolds, D. C.; Look, David C.; Jogai, B.; Litton, C. W.; Cantwell, G.; Harsch, W. C.

doi:10.1103/physrevb.60.2340

Cited by 558 publications

(329 citation statements)

References 11 publications

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“…20 The calculated value of the Γ 7 hole effective g factor of g h = −1.3 in the magnetic field parallel to the c axis (B c) is close to the value 1.2 assumed in Ref. 19 for the Γ 9 hole but has the opposite sign. On the contrary, the calculated value of the Γ 9 hole effective g factor g h ≈ 3.0 (see Ref.…”

Section: Introductionsupporting

confidence: 83%

Magneto-optical properties of bound excitons in ZnO

et al. 2004

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We present results of magneto-optical measurements and theoretical analysis of shallow bound exciton complexes in bulk ZnO. Polarization and angular dependencies of magneto-photoluminescence spectra at 5 T suggest that the upper valence band has Γ7 symmetry. Nitrogen doping leads to the formation of an acceptor center that compensates shallow donors. This is confirmed by the observation of excitons bound to ionized donors in nitrogen doped ZnO. The strongest transition in the ZnO:N (I9 transition) is associated with a donor bound exciton. This conclusion is based on its thermalization behavior in temperature-dependent magneto-transmission measurements and is supported by comparison of the thermalization properties of the I9 and I4 emission lines in temperature-dependent magneto-photoluminescence investigations.

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Section: Introductionsupporting

confidence: 83%

Magneto-optical properties of bound excitons in ZnO

et al. 2004

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“…In contrast, for N it above 5 × 10 12 cm −2 eV −1 , SFL can be considered as pinned close to mid-gap (1.7 eV where ZnO bandgap was 3.37 eV). [43] This gives the range of surface trap densities of interest for the simulation (see the Supporting Information). In the absence of quantitative information about …”

Section: Boundary Conditionsmentioning

confidence: 99%

Unveiling the Influence of Surface Fermi Level Pinning on the Piezoelectric Response of Semiconducting Nanowires

Tao

Mouis

Ardila

2017

Adv Elect Materials

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environment ever since they were first demonstrated. [4] Experimentally, it has been proved that ZnO NW based piezoelectric devices can generate a potential of a few volts. [15] This can be retrieved theoretically as long as there are no free carriers. However, experimentally prepared ZnO NWs are spontaneously n-type doped by impurities during their synthesis [16,17] and in such a case, screening by free carriers is expected to reduce drastically the piezoelectric response. There remain many such contradictions between experimental results and the present theoretical understanding of ZnO NW-based devices when realistic doping levels are considered. Chief among them are (1) decent and length-dependent performance of ZnO NWs, [18] while anticipations based on analytical and computational study showed that the output of NWs under compression were reduced to a few millivolts and presenting length-independent performance due to the screening effect; [19,20] (2) enhanced piezoelectric coefficients, [21] which were measured for ZnO NWs with diameter beyond the size effects anticipated by ab initio method; [22] and (3) dissymmetric piezoelectric response of bent nanogenerators (NGs) under tensile and compressive strain. [23] Relatively high potentials (>0.2 V) can be repeatedly obtained from NGs integrating long and large ZnO NWs [24][25][26][27] with presumably nonintentional doping. Increasing the doping concentration will reduce the generated piezopotential. [28] The nature of matrix material, as well as processing conditions, has been shown to play an important role. [24] (Table S1, Supporting Information).In this paper, we solve these contradictions by accounting for surface Fermi level pinning (SFLP). This effect commonly exists at the surface of III-V and II-VI semiconductor compounds. [29][30][31] At the surface of n-type ZnO NWs, oxygen molecules get negatively charged by capturing the free electrons from NW core. This forms a low-conductivity depletion layer near the surface, where the screening of piezoelectric potential by free carriers effect is suppressed. [30,[32][33][34][35][36] This effect has been used to neglect free carriers in most simulation studies dealing with the piezoelectric response of semiconducting nanowirebased devices. A few papers have accounted for free carriers, although without account for SFLP. [20,37] Here instead, full coupling between piezoelectric effect and semiconducting physics, including free carriers and SFLP, was considered.ZnO nanowires (NWs) are excellent candidates for the integration of energy harvesters, mechanical sensors, piezotronic and piezophototronic devices. However, ZnO NWs are usually nonintentionally n-doped during their growth. Thus, it can be expected theoretically that their piezoelectric response be degraded and mostly geometry-independent as a result of strong screening effects by free carriers, while experimentally many NW-based piezoelectric transducers demonstrate quite reasonable performance. In this paper, this apparent contradiction is explained by...

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“…Note that a deep acceptor state would not lead to an apparent quasielastic peak broadening in HREELS. In order to understand the origin of the low ionization state, we have carried out a DFT investigation by means of the hybrid density functional B3LYP, which reproduces with excellent accuracy the bulk ZnO band gap (experimental 3.44 eV [29] vs theoretical 3.38 eV).…”

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confidence: 99%

Shallow Donor States Induced by In-Diffused Cu in ZnO: A Combined HREELS and Hybrid DFT Study

et al. 2011

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A combined experimental and first principles study of Cu defects in bulk ZnO is presented. Cu particles are epitaxially deposited on the polar O-ZnOð000 " 1Þ surface at room temperature. Upon heating, a broadening of the quasielastic peak in high resolution electron energy loss spectra is observed, corresponding to an electronic doping effect of Cu atoms in bulk ZnO with an ionization energy of 88 meV. Cu impurities in ZnO, although commonly acting as acceptors, are presently observed to induce shallow donor states. We assign these to interstitial Cu species on the basis of a hybrid density functional study.

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Valence-band ordering in ZnO

Cited by 558 publications

References 11 publications

Magneto-optical properties of bound excitons in ZnO

Magneto-optical properties of bound excitons in ZnO

Unveiling the Influence of Surface Fermi Level Pinning on the Piezoelectric Response of Semiconducting Nanowires

Shallow Donor States Induced by In-Diffused Cu in ZnO: A Combined HREELS and Hybrid DFT Study

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