Crystal structures and band offsets of ultrathin HfO2–Y2O3 composite films studied by photoemission and x-ray absorption spectroscopies

Komatsu, Makoto; Yasuhara, Ryo; Takahashi, H.; Toyoda, Satoshi; Kumigashira, Hiroshi; Oshima, Masaharu; Kukuruznyak, Dmitry A.; Chikyow, Toyohiro

doi:10.1063/1.2364601

Cited by 19 publications

(13 citation statements)

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“…The increase with Gd doping in the intensity of the photoemission features in the oxygen 2 p region of the valence band, at 5 to 10 eV binding energy, relative to the Hf 4 f features at 18-21 eV binding energies, suggests that there are Gd 5d contributions to the these lower binding energy features, as is expected from studies of HfO 2 -Y 2 O 3 composite films [27]. In Figure 2, one can clearly see a shoulder on the broad photoe mission peak at the binding energy of 9-10 eV.…”

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confidence: 55%

The n-type Gd-doped HfO2 to silicon heterojunction diode

et al. 2007

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Gd-doped HfO 2 films were deposited on p-type silicon substrates in a reducing atmosphere. Photoemission measurements indicate the ntype character of Gd-doped HfO 2 due to overcompensation with oxygen vacancies. The Gd 4 f photoexcitation peak at 5.5 eV below the valence band max imum is identified using both resonant photoemission and first-principles calculations of the f hole. The rectifying (diode-like) properties of Gd-doped HfO 2 to silicon heterojunctions are demonstrated.PACS 68.55.Ln; 29.40.Wk; 81.05.Je ________________________________________ While HfO 2 has attracted considerable attention as a high-κ dielectric oxide [1][2][3][4], the gadolinium doping of a number of wide band gap semiconductors [5][6][7][8][9] suggests that Gd doping of HfO 2 may also lead to a dilute magnetic semiconduc tor [10,11]. Moreover, semiconducting Gd-doped HfO 2 may provide a promising new class of materials for neutron detec tion technologies.A gadolinium-based semiconductor diode might be better for neutron detection because of the large thermal neutron absorption cross section of gadolinium (on average ~ 46,000barns). The 157 Gd(n,γ)→ 158 Gd and 155 Gd(n,γ)→ 156 Gd reactions lead to the emission of low-energy gamma rays and conversion electrons, most of which are emit ted at energies below 220 eV [12][13][14][15]. The appeal of using 157 Gd is due to its large thermal neutron cross section of 240 000 barns [16,17]. Although sensitive to gamma radia tion, the big advantage of gadolinium over boron is not only the high neutron capture cross section but also that this cross section extends to higher neutron energies (200 meV)thanis the case for boron. While all-boron-carbide neutron detectors have been demonstrated [18][19][20], and their potential detection efficiency is much higher than that of many semiconductor materials (likely well above 50% for 10 B-enriched devices), the drawback to all boron-based devices is the need for a mod erator to reduce the neutron kinetic energies to 25-30 meV. Fissile radiation sources like 235 U or 239 Pu produce 1-2MeV neutrons, so the moderator must be significant.Since neutron capture by gadolinium leads to production of a conversion electron, the pulse height will be smaller than in the case of neutron capture by boron (10 4 charges versus 10 6 per neutron capture). Accordingly, it is advantageous to see if a Gd-doped HfO 2 diode can be fabricated that can be impedance matched and compatible with a high gain, low noise amplifier. A heterojunction diode with silicon would serve this purpose. Although Gd is expected to be a p-type dopant in HfO 2 , we attempted to fabricate a heterojunction diode of n-type Gd-doped HfO 2 with silicon by overcompen sating the Gd acceptor states by donor states introduced by oxygen vacancies, as such a device would likely have a larger depletion region and therefore larger detection volume.The Gd-doped (3 at. %) HfO 2 films were deposited on single crystal silicon (100) p-type substrates using pulsed laser deposition (PLD) at a growth rate of a...

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The n-type Gd-doped HfO2 to silicon heterojunction diode

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“…[9][10][11][12][13][14][15][16][17] However, considering the occurrence of ferroelectricity in Y:HfO 2 thin films, a simple monoclinic=cubic phase mixture or intermediate tetragonal phases seem contradictory, since neither the cubic=tetragonal nor the monoclinic phases in HfO 2 possess ferroelectric space groups. 29 A close examination of the GI-XRD diffractograms presented in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…the cubic phase. Y:HfO 2 thin films have a large bandgap, 11 are temperature stable, 21 CMOS compatible, 23,24 and due to the availability of mature atomic layer deposition (ALD) processes, 13 they are capable of conformal 3D integration. Therefore Y:HfO 2 is considered a promising material for future, highly scaled ferroelectric memories.…”

Section: Introductionmentioning

confidence: 99%

“…7 Analogous to the well-known yttrium stabilized zirconia (YSZ), 8 successful stabilization of the cubic phase in epitaxial, as well as polycrystalline Y:HfO 2 thin films has been presented by several authors. [9][10][11][12][13][14][15][16][17] Reported doping levels for complete stabilization of the cubic phase in HfO 2 range from 4 to 17 mol% YO 1.5 admixture, thereby achieving k-values of about 18 to 32.…”

Section: Introductionmentioning

confidence: 99%

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Ferroelectricity in yttrium-doped hafnium oxide

Müller

Schröder

Böscke³

et al. 2011

Journal of Applied Physics

580

351

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Structural incommensurate modulation rule in hexagonal Ba(Ti1-xMx)O3-δ (M = Mn, Fe) multiferroics AIP Advances 2, 042129 (2012) Water assisted gate induced temporal surface charge distribution probed by electrostatic force microscopy J. Appl. Phys. 112, 084329 (2012) Influence of target composition and deposition temperature on the domain structure of BiFeO3 thin films AIP Advances 2, 042104 (2012) Nanodomain structures formation during polarization reversal in uniform electric field in strontium barium niobate single crystals J. Appl. Phys. 112, 064117 (2012) The effect of the top electrode interface on the hysteretic behavior of epitaxial ferroelectric Pb(Zr,Ti)O3 thin films with bottom SrRuO3 electrode J. Appl. Phys. 112, 064116 (2012) Additional information on J. Appl. Phys. Structural and electrical evidence for a ferroelectric phase in yttrium doped hafnium oxide thin films is presented. A doping series ranging from 2.3 to 12.3 mol% YO 1.5 in HfO 2 was deposited by a thermal atomic layer deposition process. Grazing incidence X-ray diffraction of the 10 nm thick films revealed an orthorhombic phase close to the stability region of the cubic phase. The potential ferroelectricity of this orthorhombic phase was confirmed by polarization hysteresis measurements on titanium nitride based metal-insulator-metal capacitors. For 5.2 mol% YO 1.5 admixture the remanent polarization peaked at 24 lC=cm 2 with a coercive field of about 1.2 MV=cm. Considering the availability of conformal deposition processes and CMOS-compatibility, ferroelectric Y:HfO 2 implies high scaling potential for future, ferroelectric memories.

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“…5 It has been demonstrated that Y 2 O 3 doping stabilizes HfO 2 in the cubic phase. [5][6][7][8] Doping of HfO 2 by Er, [7][8][9] Gd, 8,10,11 and many other rare earth elements 8 also induces a monoclinic to cubic phase transition. The gadolinium doping of a number of wide band gap semiconductors [12][13][14] suggested that Gd doping of HfO 2 may lead to a dilute magnetic semiconductor.…”

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The electronic structure change with Gd doping of HfO2 on silicon

Losovyj

Ketsman

Sokolov

et al. 2007

Applied Physics Letters

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Gd-doped HfO2 films deposited on silicon substrates undergo a crystallographic change from monoclinic to fluorite (cubic) phase with increasing Gd concentrations. The crystallographic phase change is accompanied by a small increase in the valence bandwidth and in the apparent band offset in the surface region. Electrical measurements show pronounced rectification properties for lightly doped Gd:HfO2 films on p-Si and for heavily-doped Gd:HfO2 films on n-Si, suggesting a crossover from n-type to p-type behavior with increasing doping level.

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Crystal structures and band offsets of ultrathin HfO2–Y2O3 composite films studied by photoemission and x-ray absorption spectroscopies

Cited by 19 publications

References 15 publications

The n-type Gd-doped HfO2 to silicon heterojunction diode

The n-type Gd-doped HfO2 to silicon heterojunction diode

Ferroelectricity in yttrium-doped hafnium oxide

The electronic structure change with Gd doping of HfO2 on silicon

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