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Parameter window of diamond growth on GaN films by microwave plasma chemical vapor deposition
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Diamond & Related Materials 17 (2008) 1775 – 1779 www.elsevier.com/locate/diamond
Parameter window of diamond growth on GaN films by microwave plasma chemical vapor deposition Dipti Ranjan Mohapatra, Padmnabh Rai, Abha Misra, Pawan K. Tyagi, Brajesh S. Yadav, D.S. Misra ⁎ Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai-400 076, India Available online 16 February 2008
Abstract We report here, a detailed study of the parameter window of the deposition pressures to grow the diamond films on GaN coated quartz substrates using microwave plasma deposition technique. Hexagonal GaN films of 5 µm coated on quartz are used as substrates for diamond deposition in the pressure range of 80–140 Torr, using microwave plasma chemical vapor deposition (MPCVD) technique. The diamond films are characterized by scanning electron microscopy, XRD, photoluminescence and Raman spectroscopy. Scanning electron microscope image shows that the nucleation density of the films is high and we can deposit a continuous film for a deposition time ranging for 6–8 h. Oriented growth of diamond has been observed at higher pressure. © 2008 Elsevier B.V. All rights reserved. Keywords: Microwave plasma chemical vapor deposition; Secondary nucleation center; Pressure
1. Introduction Diamond thin films offer excellent mechanical, thermal, optical and electronic properties, and are promising candidate for high-frequency and high-power microelectronic applications. These applications require to synthesize better quality large area single-crystalline or highly oriented diamond crystals with few impurities and defects. This aspect of diamond has attracted considerable research interest in the last decades and a variety of substrates have been used for the textured growth of diamond films by CVD methods in the last decades. Promising substrates for oriented/epitaxial growth of diamond are iridium, nickel, cobalt, silicon and platinum [1–5]. GaN is another promising candidate, for use in power FETs, blue lasers and light emitting diodes. Microcrystalline diamond deposited onto GaN substrates has ability to improve the efficiency of the light emitting diode [6]. For the development of nitride based technology, a few groups have reported GaN and aluminum
⁎ Corresponding author. Tel.: +91 22 25767550; fax: +91 22 25767552. E-mail address: [email protected] (D.S. Misra). 0925-9635/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2008.02.011
nitride (AlN) growth on diamond substrates by metalorganic chemical vapor deposition [7,8]. There have been very few attempts to grow diamond on GaN using microwave plasma chemical vapor deposition (MPCVD) technique, because of the instability of GaN under typical CVD diamond process condition which results in etching of the GaN film [6]. Oba and Sugino [9,10] have used bias enhanced nucleation prior to diamond deposition onto GaN film using MPCVD. However, they could not grow a continuous film due to the low nucleation density. Recently we demonstrated growth of hexagonal diamond on hexagonal GaN films by hot filament chemical vapor deposition [11] and this promoted us to explore the various growth condition of diamond onto GaN films using MPCVD technique. In this paper, we report the deposition of continuous diamond films on GaN coated quartz substrate in a MPCVD system at different pressure. Scanning electron microscope image shows that the nucleation density of the films is high and we can deposit a continuous film for a deposition time ranging for 6 to 8 h. Our studies indicate that at higher deposition pressure (N 120 Torr), the films are (100) oriented with very minute or non-existent non-diamond impurities.
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2. Experimental
3. Results and discussion
Hexagonal GaN (h-GaN) films of 5 µm thickness are deposited on quartz substrate of the size 1 × 1cm2 in a 13.56 MHz rf magnetron sputtering apparatus described elsewhere [12]. To enhance the density of the diamond nucleation sites, the substrates were ultrasonicated in a suspension of diamond powder of 2 μm size in an acetone bath for 10 min followed by cleaning with acetone and deionized water in an ultrasonic bath. Diamond thin films are grown on the treated h-GaN thin film in microwave plasma CVD using a mixture of 0.8% methane and hydrogen concentration in the pressure range of 80–140 Torr. During growth the substrate temperature was kept at 800 °C for all the samples deposited in this study. Deposition time was 6 to 8 h, with a diamond deposition rate approximately 0.6 μm/h. The surface morphology was examined in a FEI Quanta 200 HV scanning electron microscope. Raman spectra were recorded in the range of 1000–1800 cm− 1 with a 20 mW, 514.5 nm Ar+ laser source. The photoluminescence spectra were recorded in micro-Raman instrument. XRD studies were carried out in a Philips X' pert PRO diffractometer.
Fig. 1 shows SEM images of diamond films grown on GaN substrates for 8 h by MPCVD technique at substrate temperature (Ts) of 800 °C. In the films grown at deposition pressure 80 Torr, the SEM image shows that (Fig. 1(a)) the diamond films consist of randomly oriented grains of size ranging between 300 nm to 5 µm. As evident from Fig. 1(b), as the gas pressure increases to 100 Torr, the surface morphology of the diamond film changes rapidly. Most of the grains exhibit [111] orientation with a small amount of [100] oriented grains and also the high density of secondary nucleation centers can be observed as evident in Fig. 2(a). Further increasing the deposition pressure to 120 Torr, most of the grains appear as rectangular. The [100] oriented growth dominates the surface morphology (shown in Fig. 1(c)). However a good percentage of [111] oriented grains is also visible in the image. The grain size in all the films deposited at 80, 100 and 120 Torr pressure is comparable. The density of secondary nucleation centers decreased somewhat as the pressure is increased. Fig. 1(d) shows the SEM image of the diamond film grown at 140 Torr. We can clearly visualize that the film is continuous
Fig. 1. SEM images of diamond films deposited on h-GaN films by MPCVD techniques at various deposit pressures, (a) 80 Torr, (b) 100 Torr, (c) 120 Torr and (d) 140 Torr.
D.R. Mohapatra et al. / Diamond & Related Materials 17 (2008) 1775–1779
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Fig. 2. High magnification SEM images of diamond film grown at pressure (a) 120 and (b) 140 Torr.
with mostly [100] oriented grains. The density of secondary nucleation centers is considerably reduced and also the grain size is comparatively larger. High magnification SEM images of diamond (shown in Fig. 2(a) and (b)) shows clearly that secondary nucleation decreases considerable in films deposited at 140 Torr and grains are (100) oriented dominantly.
The Raman spectra of the diamond films grown at different deposition pressure are shown in Fig. 3(a)–(d). Fig. 3(a) shows the Raman spectra of the diamond film on h-GaN film grown at pressure 80 Torr. The spectrum shows a strong intense peak centered at 1339.5 cm− 1. The peak at 1339.5 cm− 1 can be fitted to two Raman bands at 1331 cm− 1 and 1338.5 cm− 1. The band
Fig. 3. Raman spectra of diamond films on h-GaN films are grown at (a) 80 Torr, (b) 100 Torr, (c) 120 Torr and (d) 140 Torr.
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Fig. 4. X-ray diffraction spectra of diamond film on h-GaN film grown at 120 Torr.
at 1331 cm− 1 is the conventional first order Raman mode of diamond. The Raman band at 1338.5 cm− 1 corresponds to compressively distorted diamond phase [14]. A strong broad band around 1580 cm− 1 can be observed, indicating a large non-diamond component or sp2-bonded amorphous carbon incorporated into the diamond film. Fig. 3(b) and (c) shows the Raman spectra of diamond films grown at 100 and 120 Torr, respectively. The position of diamond lines appears at 1335.2 cm− 1 and 1332.1 cm− 1 for the film deposited at 100 and 120 Torr, respectively. The Raman peak (1335.2 cm− 1) of diamond film grown at 100 Torr is slightly shifted from the original peak 1332.2 cm− 1. The positive shift indicates a compressive stress in the film [13]. A broad band at 1580 cm− 1 corresponding to sp2-bonded amorphous carbon is present in all the above samples. Fig. 3(d) shows the Raman spectra of diamond films grown at 140 Torr. The characteristic diamond peak is centered at 1332.1 cm− 1 corresponding to a single phonon in brillouin zone center with a linear back ground, indicating significantly reduced non-diamond component inside the diamond film. It is quite notable, that by increasing the pressure the intensity of the Raman band at 1580 cm− 1 decreases and almost vanishes at 140 Torr pressure. It confirms that the films deposited at growth pressure 140 Torr are of higher purity. The FWHM of the diamond films grown on GaN films decreases continuously from 6.09 cm− 1 to 2.85 cm− 1 as deposition pressure increases from 80 to 140 Torr. This shows the crystalline quality of the films increases with increasing deposition pressure. The X-ray diffraction plot of diamond film deposited at 120 Torr is shown in Fig. 4. A sharp intense peak (111) is evident along with (220), (311) and (400) reflections. The relatively less intensity of (400) XRD peak is due to the low value of atomic form factor for this reflection in diamond. The FWHM of XRD peaks is sharp indicating good crystalline quality of the film. Also no reflection corresponding to GaN film is visible in XRD plot implying that the diamond film is continuous. Photoluminescence (PL) spectra of diamond film on GaN film shown in Fig. 5. The zero phonon line at 1.672 eV
corresponds to silicon impurity as reported by several authors [15–17]. The strong intensity of the peak shows that a large concentration of silicon impurity is present in our samples. This we believe is due to the etching of the quartz substrates under heating the GaN films in harsh deposition conditions of diamond. The PL band at 1.962 eV might be due to nitrogen center as was observed by Bergman et al. [15–17]. We believe that Si, O, N and perhaps Ga impurities may be present in our samples. The above results of diamond growth on GaN films show very interesting trends with the deposition pressure. The SEM images along with the Raman spectroscopy results indicate that the deposition pressure plays a very important role in the selection of the growth direction of the diamond grains. The Brillouin zone center Raman line at 1332 cm− 1 is shifted positively in the samples deposited at 80 and 100 Torr. This indicates that the cubic diamond phase in these films may be highly defective. This is also evident from the relatively strong intensity of the non-diamond Raman band present at 1580 cm− 1 in these samples. In contrast, Raman line in the films deposited at 120 and 140 Torr show almost zero shift and the nondiamond band is also relatively weaker. It may be mentioned that the Raman spectra were recorded in microscopy mode and therefore the distortion and the defects are present in the grains and not due to the grain boundaries. The film deposited at 140 Torr is substantially defect free as the shift in Raman line is minimum and the half width is very small. The half width in the films deposited at 140 Torr is comparable to single crystal diamond and the non-diamond in this sample is at the lowest. The appearance of (100) morphology with large grain size in this sample indicates that it may be promising to use single crystal GaN substrates at high growth pressure for the epitaxial diamond growth. Film deposited at 140 Torr shows microcracks at different location. It is probable due to the stress of the underlying GaN layer and high purity of 140 Torr deposited diamond. Films deposited at lower pressure contain nondiamond impurities to move flexibility in diamond structure.
Fig. 5. PL spectra of diamond film grown on GaN film, excited by 514.5 Ar+ ion laser at room temperature.
D.R. Mohapatra et al. / Diamond & Related Materials 17 (2008) 1775–1779
4. Conclusion In this work, we have studied the effect of gas pressure on the growth of diamond film on h-GaN film by MPCVD technique. Highly oriented and crystalline diamond film has been obtained at high pressure. The quality of the films increases with increasing gas pressure as was evident from the Raman spectra. The results show that the gas pressure is an important parameter influencing the crystalline and growth of diamond films. The SEM micrographs show that by changing the gas pressure secondary nucleation diminishes and the orientation of the films change rapidly. The non-diamond phase of the films decrease with the gas pressure and completely disappeared at the gas pressure 140 Torr. References [1] K. Janischowsky, M. Stammler, R. Stockel, L. Ley, Appl. Phys. Lett. 75 (1999) 2094. [2] W. Zhu, P.C. Yang, J.T. Glass, Appl. Phys. Lett. 63 (1993) 1640. [3] W. Liu, D.A. Tucker, P.C. Yang, J.T. Glass, J. Appl. Phys. 78 (1995) 1291.
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[4] T. Tachibana, Y. Yokota, K. Nishimura, K. Miyata, K. Kobashi, Y. Shintani, Diamond Relat. Mater. 5 (1996) 197. [5] K. Ohtsuka, K. Suzuki, A. Sawabe, T. Inuzuka, Jpn. J. Appl. Phys. 35 (1996) L1072. [6] P.W. May, H.Y. Tsai, W.N. Wang, J.A. Smith, Diamond Relat. Mater. 15 (2006) 526. [7] P.R. Hageman, J.J. Schermer, P.K. Larsen, Thin Solid Films 443 (2003) 9. [8] E.N. Christoph, R.M. Claudio, A.G. Jose, H. Martin, A. Oliver, E. Martin, et al., Diamond Relat. Mater. 12 (2003) 1873. [9] M. Oba, T. Sugino, Diamond Relat. Mater. 10 (2001) 1343. [10] M. Oba, T. Sugino, Jpn. J. Appl. Phys. 39 (2000) L1213. [11] Abha Misra, Pawan K. Tyagi, Brajesh S. Yadav, P. Rai, D.S. Misra, Appl. Phys. Lett. 89 (2006) 071911. [12] A. Nisha Preschilla, S. Major, N. Kumar, I. Samajdar, R.S. Srinivasa, Appl. Phys. Lett. 77 (2000) 1861. [13] M.H. Grimsditch, E. Anastassakis, M. Cadona, Phys. Rev. B 18 (1978) 901. [14] P.V. Huong, J. Mol. Struct. 292 (1993) 81. [15] L. Bergman, M.T. Mc Clure, J.T. Glass, R.J. Nemanich, J. Appl. Phys. 76 (1994) 3020. [16] Tom Feng, Bradley D. Schwartz, J. Appl. Phys. 73 (1993) 1415. [17] C.D. Clark, H. Kanda, I. Kiflawai, G. Sittas, Phys. Rev. B 51 (1995) 16681.
Diamond & Related Materials 17 (2008) 1775 – 1779 www.elsevier.com/locate/diamond
Parameter window of diamond growth on GaN films by microwave plasma chemical vapor deposition Dipti Ranjan Mohapatra, Padmnabh Rai, Abha Misra, Pawan K. Tyagi, Brajesh S. Yadav, D.S. Misra ⁎ Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai-400 076, India Available online 16 February 2008
Abstract We report here, a detailed study of the parameter window of the deposition pressures to grow the diamond films on GaN coated quartz substrates using microwave plasma deposition technique. Hexagonal GaN films of 5 µm coated on quartz are used as substrates for diamond deposition in the pressure range of 80–140 Torr, using microwave plasma chemical vapor deposition (MPCVD) technique. The diamond films are characterized by scanning electron microscopy, XRD, photoluminescence and Raman spectroscopy. Scanning electron microscope image shows that the nucleation density of the films is high and we can deposit a continuous film for a deposition time ranging for 6–8 h. Oriented growth of diamond has been observed at higher pressure. © 2008 Elsevier B.V. All rights reserved. Keywords: Microwave plasma chemical vapor deposition; Secondary nucleation center; Pressure
1. Introduction Diamond thin films offer excellent mechanical, thermal, optical and electronic properties, and are promising candidate for high-frequency and high-power microelectronic applications. These applications require to synthesize better quality large area single-crystalline or highly oriented diamond crystals with few impurities and defects. This aspect of diamond has attracted considerable research interest in the last decades and a variety of substrates have been used for the textured growth of diamond films by CVD methods in the last decades. Promising substrates for oriented/epitaxial growth of diamond are iridium, nickel, cobalt, silicon and platinum [1–5]. GaN is another promising candidate, for use in power FETs, blue lasers and light emitting diodes. Microcrystalline diamond deposited onto GaN substrates has ability to improve the efficiency of the light emitting diode [6]. For the development of nitride based technology, a few groups have reported GaN and aluminum
⁎ Corresponding author. Tel.: +91 22 25767550; fax: +91 22 25767552. E-mail address: [email protected] (D.S. Misra). 0925-9635/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2008.02.011
nitride (AlN) growth on diamond substrates by metalorganic chemical vapor deposition [7,8]. There have been very few attempts to grow diamond on GaN using microwave plasma chemical vapor deposition (MPCVD) technique, because of the instability of GaN under typical CVD diamond process condition which results in etching of the GaN film [6]. Oba and Sugino [9,10] have used bias enhanced nucleation prior to diamond deposition onto GaN film using MPCVD. However, they could not grow a continuous film due to the low nucleation density. Recently we demonstrated growth of hexagonal diamond on hexagonal GaN films by hot filament chemical vapor deposition [11] and this promoted us to explore the various growth condition of diamond onto GaN films using MPCVD technique. In this paper, we report the deposition of continuous diamond films on GaN coated quartz substrate in a MPCVD system at different pressure. Scanning electron microscope image shows that the nucleation density of the films is high and we can deposit a continuous film for a deposition time ranging for 6 to 8 h. Our studies indicate that at higher deposition pressure (N 120 Torr), the films are (100) oriented with very minute or non-existent non-diamond impurities.
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2. Experimental
3. Results and discussion
Hexagonal GaN (h-GaN) films of 5 µm thickness are deposited on quartz substrate of the size 1 × 1cm2 in a 13.56 MHz rf magnetron sputtering apparatus described elsewhere [12]. To enhance the density of the diamond nucleation sites, the substrates were ultrasonicated in a suspension of diamond powder of 2 μm size in an acetone bath for 10 min followed by cleaning with acetone and deionized water in an ultrasonic bath. Diamond thin films are grown on the treated h-GaN thin film in microwave plasma CVD using a mixture of 0.8% methane and hydrogen concentration in the pressure range of 80–140 Torr. During growth the substrate temperature was kept at 800 °C for all the samples deposited in this study. Deposition time was 6 to 8 h, with a diamond deposition rate approximately 0.6 μm/h. The surface morphology was examined in a FEI Quanta 200 HV scanning electron microscope. Raman spectra were recorded in the range of 1000–1800 cm− 1 with a 20 mW, 514.5 nm Ar+ laser source. The photoluminescence spectra were recorded in micro-Raman instrument. XRD studies were carried out in a Philips X' pert PRO diffractometer.
Fig. 1 shows SEM images of diamond films grown on GaN substrates for 8 h by MPCVD technique at substrate temperature (Ts) of 800 °C. In the films grown at deposition pressure 80 Torr, the SEM image shows that (Fig. 1(a)) the diamond films consist of randomly oriented grains of size ranging between 300 nm to 5 µm. As evident from Fig. 1(b), as the gas pressure increases to 100 Torr, the surface morphology of the diamond film changes rapidly. Most of the grains exhibit [111] orientation with a small amount of [100] oriented grains and also the high density of secondary nucleation centers can be observed as evident in Fig. 2(a). Further increasing the deposition pressure to 120 Torr, most of the grains appear as rectangular. The [100] oriented growth dominates the surface morphology (shown in Fig. 1(c)). However a good percentage of [111] oriented grains is also visible in the image. The grain size in all the films deposited at 80, 100 and 120 Torr pressure is comparable. The density of secondary nucleation centers decreased somewhat as the pressure is increased. Fig. 1(d) shows the SEM image of the diamond film grown at 140 Torr. We can clearly visualize that the film is continuous
Fig. 1. SEM images of diamond films deposited on h-GaN films by MPCVD techniques at various deposit pressures, (a) 80 Torr, (b) 100 Torr, (c) 120 Torr and (d) 140 Torr.
D.R. Mohapatra et al. / Diamond & Related Materials 17 (2008) 1775–1779
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Fig. 2. High magnification SEM images of diamond film grown at pressure (a) 120 and (b) 140 Torr.
with mostly [100] oriented grains. The density of secondary nucleation centers is considerably reduced and also the grain size is comparatively larger. High magnification SEM images of diamond (shown in Fig. 2(a) and (b)) shows clearly that secondary nucleation decreases considerable in films deposited at 140 Torr and grains are (100) oriented dominantly.
The Raman spectra of the diamond films grown at different deposition pressure are shown in Fig. 3(a)–(d). Fig. 3(a) shows the Raman spectra of the diamond film on h-GaN film grown at pressure 80 Torr. The spectrum shows a strong intense peak centered at 1339.5 cm− 1. The peak at 1339.5 cm− 1 can be fitted to two Raman bands at 1331 cm− 1 and 1338.5 cm− 1. The band
Fig. 3. Raman spectra of diamond films on h-GaN films are grown at (a) 80 Torr, (b) 100 Torr, (c) 120 Torr and (d) 140 Torr.
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Fig. 4. X-ray diffraction spectra of diamond film on h-GaN film grown at 120 Torr.
at 1331 cm− 1 is the conventional first order Raman mode of diamond. The Raman band at 1338.5 cm− 1 corresponds to compressively distorted diamond phase [14]. A strong broad band around 1580 cm− 1 can be observed, indicating a large non-diamond component or sp2-bonded amorphous carbon incorporated into the diamond film. Fig. 3(b) and (c) shows the Raman spectra of diamond films grown at 100 and 120 Torr, respectively. The position of diamond lines appears at 1335.2 cm− 1 and 1332.1 cm− 1 for the film deposited at 100 and 120 Torr, respectively. The Raman peak (1335.2 cm− 1) of diamond film grown at 100 Torr is slightly shifted from the original peak 1332.2 cm− 1. The positive shift indicates a compressive stress in the film [13]. A broad band at 1580 cm− 1 corresponding to sp2-bonded amorphous carbon is present in all the above samples. Fig. 3(d) shows the Raman spectra of diamond films grown at 140 Torr. The characteristic diamond peak is centered at 1332.1 cm− 1 corresponding to a single phonon in brillouin zone center with a linear back ground, indicating significantly reduced non-diamond component inside the diamond film. It is quite notable, that by increasing the pressure the intensity of the Raman band at 1580 cm− 1 decreases and almost vanishes at 140 Torr pressure. It confirms that the films deposited at growth pressure 140 Torr are of higher purity. The FWHM of the diamond films grown on GaN films decreases continuously from 6.09 cm− 1 to 2.85 cm− 1 as deposition pressure increases from 80 to 140 Torr. This shows the crystalline quality of the films increases with increasing deposition pressure. The X-ray diffraction plot of diamond film deposited at 120 Torr is shown in Fig. 4. A sharp intense peak (111) is evident along with (220), (311) and (400) reflections. The relatively less intensity of (400) XRD peak is due to the low value of atomic form factor for this reflection in diamond. The FWHM of XRD peaks is sharp indicating good crystalline quality of the film. Also no reflection corresponding to GaN film is visible in XRD plot implying that the diamond film is continuous. Photoluminescence (PL) spectra of diamond film on GaN film shown in Fig. 5. The zero phonon line at 1.672 eV
corresponds to silicon impurity as reported by several authors [15–17]. The strong intensity of the peak shows that a large concentration of silicon impurity is present in our samples. This we believe is due to the etching of the quartz substrates under heating the GaN films in harsh deposition conditions of diamond. The PL band at 1.962 eV might be due to nitrogen center as was observed by Bergman et al. [15–17]. We believe that Si, O, N and perhaps Ga impurities may be present in our samples. The above results of diamond growth on GaN films show very interesting trends with the deposition pressure. The SEM images along with the Raman spectroscopy results indicate that the deposition pressure plays a very important role in the selection of the growth direction of the diamond grains. The Brillouin zone center Raman line at 1332 cm− 1 is shifted positively in the samples deposited at 80 and 100 Torr. This indicates that the cubic diamond phase in these films may be highly defective. This is also evident from the relatively strong intensity of the non-diamond Raman band present at 1580 cm− 1 in these samples. In contrast, Raman line in the films deposited at 120 and 140 Torr show almost zero shift and the nondiamond band is also relatively weaker. It may be mentioned that the Raman spectra were recorded in microscopy mode and therefore the distortion and the defects are present in the grains and not due to the grain boundaries. The film deposited at 140 Torr is substantially defect free as the shift in Raman line is minimum and the half width is very small. The half width in the films deposited at 140 Torr is comparable to single crystal diamond and the non-diamond in this sample is at the lowest. The appearance of (100) morphology with large grain size in this sample indicates that it may be promising to use single crystal GaN substrates at high growth pressure for the epitaxial diamond growth. Film deposited at 140 Torr shows microcracks at different location. It is probable due to the stress of the underlying GaN layer and high purity of 140 Torr deposited diamond. Films deposited at lower pressure contain nondiamond impurities to move flexibility in diamond structure.
Fig. 5. PL spectra of diamond film grown on GaN film, excited by 514.5 Ar+ ion laser at room temperature.
D.R. Mohapatra et al. / Diamond & Related Materials 17 (2008) 1775–1779
4. Conclusion In this work, we have studied the effect of gas pressure on the growth of diamond film on h-GaN film by MPCVD technique. Highly oriented and crystalline diamond film has been obtained at high pressure. The quality of the films increases with increasing gas pressure as was evident from the Raman spectra. The results show that the gas pressure is an important parameter influencing the crystalline and growth of diamond films. The SEM micrographs show that by changing the gas pressure secondary nucleation diminishes and the orientation of the films change rapidly. The non-diamond phase of the films decrease with the gas pressure and completely disappeared at the gas pressure 140 Torr. References [1] K. Janischowsky, M. Stammler, R. Stockel, L. Ley, Appl. Phys. Lett. 75 (1999) 2094. [2] W. Zhu, P.C. Yang, J.T. Glass, Appl. Phys. Lett. 63 (1993) 1640. [3] W. Liu, D.A. Tucker, P.C. Yang, J.T. Glass, J. Appl. Phys. 78 (1995) 1291.
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[4] T. Tachibana, Y. Yokota, K. Nishimura, K. Miyata, K. Kobashi, Y. Shintani, Diamond Relat. Mater. 5 (1996) 197. [5] K. Ohtsuka, K. Suzuki, A. Sawabe, T. Inuzuka, Jpn. J. Appl. Phys. 35 (1996) L1072. [6] P.W. May, H.Y. Tsai, W.N. Wang, J.A. Smith, Diamond Relat. Mater. 15 (2006) 526. [7] P.R. Hageman, J.J. Schermer, P.K. Larsen, Thin Solid Films 443 (2003) 9. [8] E.N. Christoph, R.M. Claudio, A.G. Jose, H. Martin, A. Oliver, E. Martin, et al., Diamond Relat. Mater. 12 (2003) 1873. [9] M. Oba, T. Sugino, Diamond Relat. Mater. 10 (2001) 1343. [10] M. Oba, T. Sugino, Jpn. J. Appl. Phys. 39 (2000) L1213. [11] Abha Misra, Pawan K. Tyagi, Brajesh S. Yadav, P. Rai, D.S. Misra, Appl. Phys. Lett. 89 (2006) 071911. [12] A. Nisha Preschilla, S. Major, N. Kumar, I. Samajdar, R.S. Srinivasa, Appl. Phys. Lett. 77 (2000) 1861. [13] M.H. Grimsditch, E. Anastassakis, M. Cadona, Phys. Rev. B 18 (1978) 901. [14] P.V. Huong, J. Mol. Struct. 292 (1993) 81. [15] L. Bergman, M.T. Mc Clure, J.T. Glass, R.J. Nemanich, J. Appl. Phys. 76 (1994) 3020. [16] Tom Feng, Bradley D. Schwartz, J. Appl. Phys. 73 (1993) 1415. [17] C.D. Clark, H. Kanda, I. Kiflawai, G. Sittas, Phys. Rev. B 51 (1995) 16681.