[IEEE 2005 International Semiconductor Device Research Symposium - Bethesda, Maryland, USA...
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Student Paper Electrical characteristics of epitaxial γ-Al 2 O 3 films for quantum tunneling device The ultrathin high quality epitaxial insulating layer on Si is important for future microelectronics and thin film device, which has potential applications for quantum tunneling devices. Resonant tunneling diodes (RTDs) have been widely studied because of their potential applications in nanoscale regime for digital circuit application. For these purposes, the insulating layer needs to resolve some required properties such as high dielectric constant, good crystalline quality, and surface flatness of grown film. Al 2 O 3 has been considered to be a candidate for these applications. In previous our report, we succeed to deposit epitaxial Al 2 O 3 film on Si substrate by molecular beam epitaxy (MBE) [1] and Al 2 O 3 /Si/Al 2 O 3 /Si multiple heterostrucutes [2]. The breakdown field of the film is 8-10 MV/cm below the 4nm thickness scale. However, the properties of electrical characteristics and surface topography in various thicknesses of Al 2 O 3 films for further quantum device are not well investigated. In this study, we report the electrical characteristics with tunneling phenomena and surface topography properties of ultrathin epitaxial γ-Al 2 O 3 films in 2-10nm range. Epitaxial γ-Al 2 O 3 films were fabricated on the n-type Si (111) substrates by mixed source MBE method, aluminum as a solid source and N 2 O as a gas source. Details of Al 2 O 3 fabrication process are described previous report [3]. The crystalline property of the epitaxial γ-Al 2 O 3 films was studied by RHEED as shown in Fig. 1. AFM images show that the surface begins to appear the small protrusions as increasing thicknesses as shown in Fig. 2. However it means that the surface roughness is equivalent to atomic level. We investigate the electric characteristics of epitaxial Al 2 O 3 films in 2-10nm thickness. In this region of thickness may apply to quantum tunneling device as RTD and field emitter (FE) [4]. The characteristics of current density-voltage (J-V) and current density-electric field (J-E) observed its breakdown field as 6-12 MV/cm with low leakage current as shown in Fig 3. Tendency to the change of the breakdown voltage is increased as the film thickness but it decreases the electric field at breakdown voltage. The dependence of leakage current density on applied field for epitaxial Al 2 O 3 films is shown fig 4. The leakage current density reduces with the increase of Al 2 O 3 thickness. Al 2 O 3 films led to low leakage current density of ～10 -7 A/cm 2 at a field of 3MV/cm. The change of the current shows that the conduction process is similar to the Fowler-Nordheim (F-N) tunneling characteristics. F-N tunneling plot was performed as shown figure 5. In this F-N plot, a straight line portion was observed which indicates the presence of the F-N tunneling phenomenon. The conduction band offset (⊿Eｃ) is from 2eV to 2.5eV. The obtain value is sufficiently large to create potential barrier for quantum device without a large leakage current. These high qualities of electrical dielectric properties and tunneling properties with good topography for epitaxial γ-Al 2 O 3 are considered suitable for a quantum tunneling device. Reference [1] H. Wado, T. Shimizu, and Makoto Ishida, Epitaxial growth of γ-Al2O3 layers on Si(111) using Al solid source and N2O gas molecular beam epitaxy, Appl. Phys.Lett. 67 (15), 9 Oct 1995. pp 2200-2202 1-4244-0084-8/05/$20.00/©2005 IEEE
Transcript of [IEEE 2005 International Semiconductor Device Research Symposium - Bethesda, Maryland, USA...
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Student Paper
Electrical characteristics of epitaxial γ-Al2O3 films for quantum tunneling device
The ultrathin high quality epitaxial insulating layer on Si is important for future microelectronics and
thin film device, which has potential applications for quantum tunneling devices. Resonant tunneling
diodes (RTDs) have been widely studied because of their potential applications in nanoscale regime for
digital circuit application. For these purposes, the insulating layer needs to resolve some required
properties such as high dielectric constant, good crystalline quality, and surface flatness of grown film.
Al2O3 has been considered to be a candidate for these applications. In previous our report, we succeed
to deposit epitaxial Al2O3 film on Si substrate by molecular beam epitaxy (MBE) [1] and
Al2O3/Si/Al2O3/Si multiple heterostrucutes [2]. The breakdown field of the film is 8-10 MV/cm below
the 4nm thickness scale. However, the properties of electrical characteristics and surface topography in
various thicknesses of Al2O3 films for further quantum device are not well investigated. In this study,
we report the electrical characteristics with tunneling phenomena and surface topography properties of
ultrathin epitaxial γ-Al2O3 films in 2-10nm range.
Epitaxial γ-Al2O3 films were fabricated on the n-type Si (111) substrates by mixed source MBE
method, aluminum as a solid source and N2O as a gas source. Details of Al2O3 fabrication process are
described previous report [3].
The crystalline property of the epitaxial γ-Al2O3 films was studied by RHEED as shown in Fig. 1.
AFM images show that the surface begins to appear the small protrusions as increasing thicknesses as
shown in Fig. 2. However it means that the surface roughness is equivalent to atomic level. We
investigate the electric characteristics of epitaxial Al2O3 films in 2-10nm thickness. In this region of
thickness may apply to quantum tunneling device as RTD and field emitter (FE) [4]. The characteristics
of current density-voltage (J-V) and current density-electric field (J-E) observed its breakdown field as
6-12 MV/cm with low leakage current as shown in Fig 3. Tendency to the change of the breakdown
voltage is increased as the film thickness but it decreases the electric field at breakdown voltage. The
dependence of leakage current density on applied field for epitaxial Al2O3 films is shown fig 4. The
leakage current density reduces with the increase of Al2O3 thickness. Al2O3 films led to low leakage
current density of ～10-7 A/cm2 at a field of 3MV/cm. The change of the current shows that the
conduction process is similar to the Fowler-Nordheim (F-N) tunneling characteristics. F-N tunneling
plot was performed as shown figure 5. In this F-N plot, a straight line portion was observed which
indicates the presence of the F-N tunneling phenomenon. The conduction band offset (⊿Eｃ) is from
2eV to 2.5eV. The obtain value is sufficiently large to create potential barrier for quantum device
without a large leakage current. These high qualities of electrical dielectric properties and tunneling
properties with good topography for epitaxial γ-Al2O3 are considered suitable for a quantum tunneling
device.
Reference
[1] H. Wado, T. Shimizu, and Makoto Ishida, Epitaxial growth of γ-Al2O3 layers on Si(111) using Al solid source and N2O gas
molecular beam epitaxy, Appl. Phys.Lett. 67 (15), 9 Oct 1995. pp 2200-2202
1-4244-0084-8/05/$20.00/©2005 IEEE
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Student Paper
[2] Md. Shahjahan, Y. Koji, K. Sawada and M. Ishida, Fabrication of resonance Tunnel Diode by γ-Al2O3/Si Multiple
Heterostrucutes, Jpn. J. Appl. Phys. Vol. 41 (2002) pp. 2602-2605
[3] Y-C. Jung, H. Miura and M.Ishida, Formation of Very Thin Epitaxial Al2O3 Prelyaer with Very Smooth Surface on Si(111)
Using a Protective Oxide Layer, Jpn. J. Appl. Phys. Vol. 38 (1999) pp.2333-2336
[4] J-S. Kim, T. Hoshi, K. Sawada and M. Ishida. Planar metal-insulator-semiconductor type field emitter fabricated on an
epitaxial Al/Al2O3/Si (111) structure, J. Vac. Sci. Technol. B 22(3), May/June 2004. pp. 1358-1361
0 2 4 6 810-1010-910-810-710-610-510-410-310-210-1100101102103
2nm 4.5nm 5.5nm 8.5nm 10nm
Cur
rent
den
sity
, J [A
/cm
2 ]
Applied Voltage [V]
-2 0 2 4 6 8 10 1210-9
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
102
J-2nm J-4.5nm J-5.5nm J-8.5 J-10nm
Cur
rent
den
sity
, J [A
/cm
2 ]
Electric field,E [MV/cm]
2nm 4.5nm 5.5nm 8.5nm 10nm
10-7
10-6
Cur
rent
den
sity
, J[A
/cm
2 ]
Toxide
J @ 3MV/cm
0.0 0.1 0.2 0.3 0.4 0.510-8
10-7
10-6
10-5
10-4
10-3
2nm 4.5nm 5.5nm 8.5nm 10nm
J/E2
1/E
Fig. 1. RHEED pattern of Al2O3 films as 2nm (a) and 8nm
thickness (b)
Fig. 2. 1µm scale AFM images of Al2O3 film. (a) 2nm
thick, RMS=0.31nm, Z range=5.73nm (b) 8nm thick,
RMS=1.22nm, Z range=13.74nm
Fig. 3. The characteristics of current density-voltage (a) and current density-electric field (b)
Fig. 4 Leakage current density versus thickness at applied
field of 3MV/cm
Fig. 5. F-N tunneling characteristics
(a) (a) (b) (b)
(a) (b)
