Electron Velocity of 6×107 cm/s at 300 K in Stress Engineered InAlN/GaN Nano-Channel High-Electron-Mobility Transistors
Supporting Data
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2
Source Resistance :
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Figure S1 shows the ratio of measured Rs/Rs0 as a function of ID for InAlN/GaN
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NC Fin-HEMTs and conventional HEMTs. Both Fin-HEMT and conventional HEMT are
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exhibiting similar behaviour of Rs/Rs0 versus IDS which is different from the previous
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report [1].
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D
Rs/Rs0at ID= 0A/mm
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50m(Conv.HEMT)
400nm (Fin-HEMT)
934nm (Fin-HEMT)
1074nm (Fin-HEMT)
IDS
5
4
Ig
G
S
3
2
1
0.0
0.5
1.0
1.5
IDS[A/mm]
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8
9
10
Figure S1. The ratio of measured source resistance (Rs) and Rs0 measured at ID=0
A/mm versus IDS. Inset shows the setup to measure Rs at different IDS.
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Micro-PL and micro-Raman measurements:
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To study the stress in the formed InAlN/GaN NC with and without SiN stress
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layer, micro-Photoluminescence (PL) and micro-Raman measurements were carried out
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using a Jobin Yvon LABRAM HR system equipped with CCD detector and a X-Y
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mapping stage. The UV spectral mapping is done by using a high magnification
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objective lens with laser spot size <1.0 µm under 325 nm He-Cd laser excitation line.
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The laser power on the surface was kept very low to avoid peak shift due to surface
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temperature. To resolve spectral line shape on the nano-patterned channel, line scan
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measurements across the channel is carried out with ~100 nm step setting in the
Supplementary Data (L14-07875R2)
Electron Velocity of 6×107 cm/s at 300 K in Stress Engineered InAlN/GaN Nano-Channel High-Electron-Mobility Transistors
1
scanner. Raman spectra are recorded from the patterned channel to check variation in
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line shapes of optical phonon peaks.
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Line-scan of micro-PL measurements:
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The micro-PL (µPL) spectrum of the patterned nano-channel (NC) without SiN
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passivation layer indicates the nature of the near-band-edge PL shifts when NC is
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completely surrounded by the SiN layer (See Figure S2). The room temperature PL
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spectra show a dominant near-band edge transition with a line shape broadening
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toward the low energy side. The improved PL intensity observed from the top of NC is
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attributed to the reduction of surface defect density and extraction of strong PL by light
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scattering from the sidewalls of the NC (patterned region). The intensity is lower in the
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mesa etched region due to plasma induced damage and point defects formation. The
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increased intensity from the surface of the HEMT stack from patterned region helps to
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distinguish the formed NC from the mesa etched region.
30x10
(a)
E~16.5 meV
50x10
(b)
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InAlN/GaN w/o SiN
3.400
Energy [eV]
25
3.395
3
3.405
InAlN/GaN with SiN
PL Intensity [a.u.]
Energy [eV]
3.400
3
3.395
3.390
15
3.385
10
3.380
5
3.380
0
3.375
40
E~2.7 meV
30
3.390
20
3.385
~30900
PL Intensity [a.u.]
3.405
10
~25478
3.375
1
2
3
Position[m]
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0
1
2
3
Position[m]
4
15
16
17
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Figure S2. Micro-PL line-scan results from the InAlN/GaN NC (a) with and (b) without
SiN passivation.
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The peak shift of about 16.5 meV is clearly seen in the micro-PL line scan of SiN
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passivated NC region as seen from this Fig. S2. We have carried out repeated line
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scans and we observed about ~10 meV additional peak shift of the SiN covered NC with
Supplementary Data (L14-07875R2)
Electron Velocity of 6×107 cm/s at 300 K in Stress Engineered InAlN/GaN Nano-Channel High-Electron-Mobility Transistors
1
respect to the SiN covered conventional HEMT surface. Therefore, based on the PL
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peak shift vs. in-plane stress relationship, an additional in-plane stress component of
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about 0.47 ± 0.02 GPa can be estimated. Similarly, red-shift was also reported in
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AlGaN/GaN HEMT structure with SiN passivation [2]. The NC with additional in-plane
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tensile stress can also produce polarized charges at the side walls that can lead to the
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increase of 2DEG carrier density. There is a huge increase in the current density in the
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InAlN/GaN NC Fin-HEMT observed in our experiment {See Figure 2(a) and (b)}.
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Therefore, beside the contribution of in-plane stress in the channel region, the increased
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carrier density could also be due to a modified band bending at the InAlN/GaN NC
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sidewalls covered with SiN and the creation of positive charges at these SiN/InAlN/GaN
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NC interfaces may lead to higher current density as compared to conventional planar
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InAlN/GaN HEMTs. The decrease of sheet resistance with the increase of tensile stress
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was also realized on InAlN/GaN nano-ribbon by finite element models [3]. The stress
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under the T-gate regions {see regions (i) and (ii) in Fig 1(c)} can be even higher than the
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regions {see inset of Fig 4(b)} subjected by micro-PL measurements. The stresses
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under the T-gate regions are difficult to measure using optical techniques. Due to the
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resolution limit of spectrometer in UV-Raman, the accuracy of estimated stress
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component is lower than the estimated stress component by line-scanned micro-PL
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(0.47±0.02 GPa) which offers a higher spectral resolution map {see Fig 4(a) and (b)}.
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Therefore, more experimental studies needed to address the observations in such Fin-
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HEMTs.
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References
[1] D.S.Lee, H.Wang, A.Wu, M.Azize, O.Laboutin, Y.Cao, J.W.Johnson, E.Beam,
A.Ketterson, M.L.Schuette et al., IEEE Electron Device Lett., 34, 969 (2013).
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[2] C.M.Jeon and A.-L.Lee, Appl. Phys. Lett., 86, 172101 (2005).
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[3] E.J.Jones, M.Azize, M.J.Smith, T.Palacios and S.Gradecak, Appl. Phys. Lett.,
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101, 113101 (2012).
Supplementary Data (L14-07875R2)