American Journal of Anal yt ical Chemistry, 2011, 2, 984-988
doi:10.4236/ajac.2011.28115 Published Online December 2011 (http://www.SciRP.org/journal/ajac)
Structural and Electrical Characterization of GaN Thin
Films on Si(100)
Gajanan Niranjan Chaudhari*, Vijay Ramkrishna Chinchamalatpure, Sharada Arvind Ghosh
Nanotechnology Research Laboratory, Shri Shivaji Science College, Amravati, India
Received July 13, 2011; revised September 23, 2011; accepted October 5, 2011
Abstract
The Gallium Nitride (GaN) layers grown on silicon substrates by electron beam evaporation technique. X-
ray diffraction revealed that polycrystalline GaN was obtained indicating the enhance crystallinity of the
films with annealing temperature at 600˚C. Crystalline quality of the GaN films was determined by Scanning
Electron Microscopy (SEM). The crystalline size increases with increasing annealing temperature. The fab-
ricated MIS structures were characterized using Capacitance-Voltage (C-V) measurements, the capacitance
remains nearly constant over a large range in higher negative as well as over a large range in higher positive
gate voltages and Current-Voltage (I-V) measurements shows low forward and reverse current possibly due
to high density defect formation in the thin layer of gallium nitride during its growth.The film is character-
ized by X-Ray photoelectron spectroscopy (XPS). The XPS spectra show that formation of pure GaN with-
out presence of elemental gallium and Ga2O3 in this film.
Keywords: Electron Beam Evaporation Technique, GaN Thin Film, C-V, I-V
1. Introduction
GaN (Gallium Nitride) have attracted interest due to their
wide and direct band gap and their potential application
to blue-ultraviolet light emitting devices, short-wave-
length optoelectronic devices and high-power electrical
devices [1]. Silicon is increasingly being used as a sub-
strate for GaN growth [2,3] GaN deposited on silicon (Si)
substrates has great advantages including excellent wafer
quality, less hardness and more design flexibility with
current silicon electronic circuit system [4-6]. The Si
substrate for GaN growth has some advantages over
other substrates. It can be obtained at low cost and the
well developed Si growth technology ensures high qual-
ity p- and n-type Si wafers. Furthermore, the het-
ero-epitaxial system of GaN on Si substrate can poten-
tially combine the optoelectronic properties of GaN with
those of highly advanced Si electronic devices. Direct
growth of a GaN film on Si substrate results in either
polycrystalline growth or a substantial diffusion of Si
into the GaN film. Direct growth of a GaN film on Si
substrate results in either polycrystalline growth or a
substantial diffusion of Si into the GaN film. Thin AlN
films have been used as buffer layers for GaN growth on
Si substrate [7,8]. Threading dislocations and inversion
domain boundaries usually form at the early stage of
growth and then propagate through the film surface [9].
The initial growth mode and microstructure strongly de-
pend on types of buffer layers [10-13], growth conditions,
and growth methods [14-19]. Until now, little effort has
been made to study the initial growth of GaN under dif-
ferent growth conditions.
2. Experimental Details:
The GaN thin films were grown on Si(100) substrates by
using electron beam evaporation method. Si(100) was
chosen due to its trigonal symmetry favoring epitaxial
growth of the GaN(0001) plane. The substrate was
cleaned by 5% HF solution prior to the epitaxial growth.
After a chemical cleaning process, the Si(100) substrate
was heated to 1000˚C under hydrogen ambient for 10
min to produce a clean, oxide-free surface to prevent the
melt back etching of Si substrate.
The filament is used to activate the nitrogen gas and
e-beam for evaporating gallium, water circulation is used
for cooling purposes in a reaction chamber. The sub-
strates are kept at a distance of 10 cm above the gallium
source which is evaporated by electron beam. There is a
tungsten filament heated at 2000˚C by a dc supply in

G. N. CHAUDHARI ET AL.985
between gallium source and the substrates to activate the
nitrogen gas the nitrogen gas is directed on to the hot
filament. The GaN experimental samples were grown at
room temperature, 300˚C and 600˚C. The thickness of
thin film GaN was 250 nm, The contact of as-grown
sample was deposited by e-gun evaporator. The anneal-
ing process was carried out at 800˚C for 2 minutes to
activate the sample and to provide the contact ohmic.
The constant pressure 7 × 10–5 Torr was maintained
through out the deposition. The gallium was evaporated
using an e-beam of energy and current 100 mA. About
200 nm thick film of GaN were deposited on Si at the
rate of 0.2 nm/s. Thickness was controlled by using a
water cooling arrangement.
3. Result and Discussion
Figure 1 shows the X-ray diffraction (XRD) spectra of
the GaN layer grown on Si substrates. The pattern for
film grown at 300˚C only reveal substrate peaks at 33.2°
and 69.3˚ which correspond to Si(200) and Si(400)
planes respectively. No X-ray diffraction peak corre-
sponding to the crystalline phase of GaN was detected,
suggesting an amorphous structure.
For the GaN film grown at 600˚C, weak peak was ob-
served at 34.4˚ which corresponds to (002) hexagonal
wurtzite crystalline GaN. X-ray diffraction peaks ob-
served for GaN is in good agreement with JCPDS data of
the hexagonal crystalline GaN. The presence of strong
and sharp GaN crystalline peaks were observed with
increasing annealing temperature, the measured diffract-
tion peaks do not change significantly, but the intensity
of these peaks becomes greater and sharper. This is due
to the crystallite sizes becoming larger with evaluating
Figure 1. XRD Spectra of GaN thin film on Si (100) sub-
strates annealed at (a) 300˚C and at (b) 600˚C.
the annealing temperature, these films are a mixed phase
of crystalline and amorphous structure. This is probably
a signature of the microcrystalline phase for GaN. The
crystalline (grain) size determined is about 167 nm, thus
confirming the microcrystalline structure of the films.
Figure 2(a) shows the surface morphology of the
samples by using SEM, there are small grains in the film
annealing at 300˚C. This indicates that the mobility of
Ga atoms is not large enough to make the grains grow
large, so the crystallite size is limited by the diffusion
length of Ga atoms. Figure 2(b) shows the pattern of the
film that was grown at 600˚C. It can be seen that the
crystalline size is larger than that of films shown in Fig-
ure 2(a) This is because the mobility of Ga atoms be-
comes larger with the increasing annealing temperature,
thus it is possible to form larger grains. In the same way,
the grains shown in Figure 2(b) are much larger than
those in Figure 2(a) due to the higher annealing tem-
perature. The grain size of the films is found to be about
200 nm in Figure 2(b).
(a)
(b)
Figure 2. SEM micrograph of GaN thin film annealed at (a)
300˚C and at (b) 600˚C.

G. N. CHAUDHARI ET AL. 986
Figure 3 shows FTIR pattern for the sample (nitri-
dated at 600˚C, 8 h) a clear absorption peak at 600 cm−1
due to GaN bond stretch was presented. It has been re-
ported that GaN absorbs infrared light at near 1100 cm−1
with shoulder at 1200 cm−1 due to Si-O bond stretching
vibration and at 816 and 446 cm−1 due to ring structure.
All the above I R absorptions of pure Si are identified in
the spectrum of composite at 1220, 900, 600 and 460
cm−1 respectively. No other strong peaks were presented
in the pattern. It indicated that the element Ga domi-
nantly existed with Ga-N bond in the samples.
4. Electrical Characterization
Figure 4 shows the capacitance-voltage (C-V) meas-
urements of the fabricated MIS structures at room tem-
perature, 300˚C and 600˚C on the GaN thin film depos-
ited at 650˚C. It is observed that, the capacitance remains
nearly constant over a large range in higher negative as
well as over a large range in higher positive gate voltages
indicating a formally pinned surface. However, the ca-
pacitance was found to be higher in the negative but
lower in the positive gate voltage. Further the capaci-
tance was found to be higher for the thin film GaN at
300˚C in both the zones. The sudden decrease in capaci-
tance at 0 V is due to defect density in the film and also
due to the semiconductor fermi level is not properly
pinned at the interface. These measurements demonstate
that the Al/GaN/Si(111) system possesses the charge
control needed for insulated gate field effect transistor
operation with a higher dielectric constant.
In this study, Current -Voltage (I-V) measurements
were made on MIS structure fabricated by evaporating
2000A˚ of Al on GaN layers deposited on Si(100) sub-
strate. Figure 5 shows the results of a typical measure-
ment performed at 300˚C. The Current-Voltage charac-
teristics shows low forward and reverse current possibly
Figure 3. FTIR Spectra of GaN thin film as deposited.
Figure 4. C-V characteristics of GaN thin film on Si at dif-
ferent temperature (a) as deposited (b) at 300˚C (c) at
600˚C.
Figure 5. The I-V characteristics of GaN thin film at 300˚C.
due to high density defect formation in the thin layer of
gallium nitride during its growth. The leakage current is
high at 300˚C, had not damaged the sample. The actual
nature of the metal-semiconductor contact is not control-
lable and in fact may vary substantially from one process
to another.
Figure 6 shows the room temperature photolumines-
cence spectra of GaN film which was annealed at 300˚C.
The PL spectrum shows an emission at 353 nm (3.5 eV)
for room temperature measurement. The resulting film
exhibits a blue-shift in the optical band gap relative to
GaN (3.4 eV). It may be explained by quantum confine-
ment model [20]. Both the optical excitation and recom-
bination take place in the nanometer grain, and the en-
ergy gap of the grain is enlarged due to the quantum con-

G. N. CHAUDHARI ET AL. 987
Figure 6. The photoluminesce spectra of GaN.
finement effect. In addition, two other emissions can be
observed, which peaked at 446 nm and 472 nm respect-
tively. The 446 nm peak results from radiative recombi-
nations related to the tail region, and the other peak
comes from localized states which are attributed to deep
traps like nitrogen vacancies [21].
Figure 7 shows the X-ray photoelectron spectra of N
1s, Ga 2p and Ga 3d for films grown at the annealing
temperature of 600˚C. As can be observed, the N 1s sig-
nal shown in Figure 7(a) contains a main peak centered
at 397.5 eV. The width and slight asymmetry of the N 1s
peak is attributed to the possible presence of nitrogen in
GaN [22]. Ga 2p3/2 and Ga 2p1/2 peaks are shown in Fig-
ure 7(b) with binding energies of 1117 and 1143.2 eV
respectively. The core level values of gallium were found
to have a positive shift with respect to elemental gallium.
Dinescu et al. [23] and Elkashef et al. [22] have reported
the values of the Ga 2p3/2 peak at 1117 eV and 1119.2 eV
in their GaN films respectively. Figure 7(c) shows Ga 3d
spectra for the films. No bond formation between Ga and
O was observed since the Ga 3d spectrum did not show
any peak corresponding to Ga2O3 as reported by Ishikaua
et al. [24]. The above results confirm the formation of
pure GaN without the presence of elemental gallium and
Ga2O3 in this film.
5. Conclusions
GaN thin film has been deposited on Si (100) by using
electron beam evaporation method. The GaN/Si (100)
structures were studied by structural and electrical char-
acteristics. The XRD and SEM of GaN/Si(100) indicates
the enhance crystallinity of the films with annealing
temperature at 600˚C. The C-V measurement of GaN
thin film deposited on Si(100) annealed at 600˚C shows
large frequency dispersion in the accumulation region. The
Current-Voltage (I-V) measurement shows low forward
and reverse current possibly due to high density defect
Intensity (a.u.)
396398400 402
394
397.5 eV
Binding energy/eV
(a)
1120 1130 1140 11501110
1117 eV
Binding energy/eV
Ga2P
3/2
Ga2P
1/2
Intensity (a.u.)
(b)
Ga3d
Intensity (a.u.)
20 25
15
Binding energy/eV
(c)
Figure 7. It shows the XPS spectra of GaN thin film on Si (a)
N 1s; (b) Ga 2p; (c) Ga 3d peaks for the film.
formation in the thin layer of gallium nitride during its
growth. The XPS spectra show that formation of pure
GaN without presence of elemental gallium and Ga2O3 in
this film.
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