QW_EU

Report
Peter Deák, professor of physics
Department of Atomic Physics Surface
,
Physics Laboratory
Budapest University of Technology and Economics
Budafoki út 8. , Budapest H-1111, Hungary
Tel. 463-4207
Fax 463-4357
E-mail: [email protected]
Proposal for an FP6 STREP FET
based on nanodevice ideas with SiC
Information Society Technologies
2003-2004 Workprogramme
2/3 of the budget will be devoted to IPs and NoEs.
HOWEVER
On average two to three IPs and NoEs are expected to be
supported for each Strategic Objectiv.
The IST thematic priority will also support
Specific Targeted Research Projects (STREPs)
several STREPs are also foreseen in most objectives.
IST will support research into future visions
and emerging technologies (FET).
All instruments should have adequate industrial participation.
The selection criteria and weights and thresholds for the FET
open scheme are different.
Scientific and technological excellence, Potential impact,Quality of the consortium
The Community support for IST in FP6 will help mobilise the
industrial and research community around high-risk long term
goals.
2.3.1.2 Micro and nano systems
Additional STREPs will be restricted to explore highly
promising alternative approaches to prepare new
technological fields
to explore the application potential of micro-nano technology
Nano-devices with SiC
Ideas of a theorist:
1. EXPERIMENT
Heat treatment of a SiO2/Si system of electronic quality in a CO
containing gas:
CO diffusion  dissociation  SiC formation at SiO2/Si interface.
SUBSTRATE: Si (100); P- or N-doped (4-6 cm).
OXIDE: 100 nm, thermally grown at 1050 °C in dry oxygen,
Quality: density of electrically active states in the oxide and at
the interface < 5·1010 cm-2 (CV)
TREATMENT: furnace anneal in Ar gas flow of 100 cm3/min,
containing 5 % CO (gas purity: 99.995%)
- for 3, 8 and 20 hours
- between 900-1190C
Characterization of samples by: SIMS, XPS, TEM, AFM, ESR, CV
SiC is present in form of cubic crystallites at the interface:
3 hours
20 hours
45  45  20 nm
90  90  35 nm
ratio of average grain volumes: 7 (reaction limited growth)
nucleation density, 2.5109 cm-2, independent of time
About 90 % of the crystallites are epitaxially oriented:
Orientation of the grains:
Top view
(001)Si || (001)SiC
[110]Si || [110]SiC
Side view
There are no voids at the Si/SiO2 interface!
SiC
4 : 5 fit between lattice constants:
ESR: dangling bond density ~ 41012 cm-2
(courtesy of M. Brandt, TU-Munich)
LIKELY GROWTH MECHANISM
CO
1
O
C
2
SiO2
SiC
O
C
3
O
C
Si
1.
2.
3.
(CO) + 2 <SiO2>  <SiO2:Ci,Oi> loss of ~ 7 eV/CO (K
et al. PRB 2001)
2 (CO) + 2 <SiO2>  2 <SiC> + 3(O2) loss of ~ 8 eV/CO ; V=-63 Å3
4(CO) + 6 <Si>  4 <SiC> + 2<SiO2> gain of ~ 6 eV/CO ; V=+48 Å3
AFM after etching off the SiO2 layer shows etch pits at the Si/SiC interface:
Together with lateral growth direction and shape of the cross section,
proof for CO dissociation at the Si/SiC interface!
GRAINS COALESCENCE WITHOUT GRAIN BOUNDARY
IDEA 1.a
SiO2
Si (SOI)
SiO2
Si
Band structure:
C
V
SiC
Problems to be solved (before thinking of devices)
1. Lateral growth rate: depends only on [CO] and T
- growth volume is linear with time
growth rate T =1100 C; pCO  0.10 atm
- T (> 1000 C) is critical
 0.12
growth rate T =1190 C; pCO  0.05 atm
- Rate with 1.00 atm CO2 at 1190 C is the same as with 0.05 atm CO
but quality somewhat worse
2. Control of nucleation: presently random
- density independent of process parameters: ~ 2.5 ·109 cm-2
- suspicion: depends on defects at interface (irradiation in pattern?)
3. During long anneals the oxide degrades
4. Passivation of dangling bonds:
- dangling bond density corresponds to 4:5 lattice parameter ratio
- “wet” treatments had no effect
IDEA 1.b
SiO2
Si
Band structure:
C
V
SiC
IDEA 1.+ (on the side)
Nucleation process for 3C-SiC heteroepitaxy
2. EXPERIMENT
ALE of SiC:
- monolayer growth of 3C-SiC on Si in ALE proven [Hara et
al. Thin Solid Films 225, 240 (1993)]
- monocrystalline growth was possible even on Si in a
commercial planetary reactor [Sumakeris et al., ibid. p. 219;
Nagasawa & Yamaguchi, ibid. p.230]
- layer by layer 3C- SiC homoepitaxy in ALE demonstrated
[Fuyuki et al., ibid. p. 225]
2. THEORY
Calculation of the stability and electronic structure of various extended
defects in SiC: alternating layer sequences in SiC.
C
Si
C
C
Si
Si
Si
C face substrate
Si face substrate
ALE layers with polarity change
ALE layers with polarity change
Si
C
Si
Si
C
C
C
C
Si
3.6 eV
1.8 eV
1.4 eV
0.3 eV
~ 3Å
~ 2Å
Based on bulk band off-sets, strong QW effect expected.
No stress in the system!
Methods: ab initio DFT electronic structure calculations; DFTB-MD
- DFTB-MD: if the “homo-double-layers” are formed during ALE,
H
H
they are stable up to temperatures where
surface H is released
Si
C
Si
C
Si
C
C
Si
Si
C
Studies regarding stability during growth
(attack of single CH3 on Si-C-Si-Si-H
and of SiH3 on C-Si-C-C-H sequence)
are under way.
- ab initio DFT: to keep periodicity, both type of “homo-doublelayers” have to be built in into the supercell.
C
C
Si
C
Si
Si
C
Si
Si
Si
C
C
C
Si
C
Si
> 4 eV
2.9 eV
??
~ 5A
Wave
function at
the VB edge:
(LDA problem with CB)
1.0 eV
Further possibilities…to be
examined by calculations
Admittedly: it is a long shot before thinking of devices
but
IST will support research into future visions (FET) and
FP6 will help mobilise around high-risk long term goals.
So, while theory is working:
- why not study ways to use such systems
- why not study problems of contacting, integrating, etc.
- why no try to grow it with ALE!?!?
Device ideas?????
• HEMT ?
• Idea on the side: blocking of stacking fault motion in SiC!
Possible distribution of tasks
Managment
FhG-IIS-B
nano SiC in Si/SiO2 synthesis
MFA + FhG-IIS-B
QW within SiC synthesis
UE(Ley)
Theory
BUTE + UPB
structural characterization
MFA + BUTE+ UE(Ley)
electrical/optical.EPR characterization
Ue(Pensl) + LiU
Device considerations
FhG-IIS-B, MFA, LiU/Laussane
"interested industry"
???

similar documents