- Email: [email protected]
(1 1 1)Si substrates
Sensors and Actuators A 147 (2008) 1–5
Contents lists available at ScienceDirect
Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna
GaN UV MSM photodetector on porous -SiC/(1 1 1)Si substrates Shiuan-Ho Chang a,∗ , Yean-Kuen Fang b , Kai-Chun Hsu b , Tzu-Chieh Wei b a b
Department of Computer and Communication, Diwan University, Madou Town, Tainan 721, Taiwan VLSI Technology Laboratory, Institute of Microelectronics, Department of Electrical Engineering, National Cheng Kung University, Tainan, Taiwan
a r t i c l e
i n f o
Article history: Received 22 December 2007 Received in revised form 22 February 2008 Accepted 11 March 2008 Available online 20 March 2008 Keywords: GaN Porous -SiC MSM
a b s t r a c t This paper reports the GaN thin films grown on Si substrates by MOCVD with different buffer layers, i.e., cubic -SiC and porous -SiC (PSC). The -SiC thin films were prepared with RTCVD, while the PSC thin films were fabricated by electrochemical anodization method on cubic -SiC thin films, as well as the PL spectrometer, HRXRD and SEM were employed to analyze the samples. Furthermore, a metal–semiconductor–metal (MSM) photodetectors using GaN films grown on -SiC/Si and porous -SiC/Si were developed. For GaN/PSC/Si, we found a very high photo/dark current ratio of 2427.23, which is about 60 times the value of GaN/-SiC/Si, thus evidenced the PSC indeed can help low leakage current and high-quality GaN thin films grown on Si substrates. © 2008 Elsevier B.V. All rights reserved.
1. Introduction It is necessary to develop ultraviolet (UV) detectors for sensing rapidly mature InGaN LEDs and laser, causing the UV detectors have been employed for flame monitoring, pollution analyzers, UV astronomy, and medical instruments [1]. Recently, there are great investigations of electronics and optoelectronics based on the group III nitride material systems for their high thermal conductivity, robust chemical bonding, high breakdown field strength and the established hetero-structure epitaxy technologies [2]. In the group III nitride materials system, GaN is one of the most important wide band gap semiconductor due to its numerous applications in ultraviolet-blue optical devices. However, GaN is generally grown on sapphire or silicon carbide substrates, which are not only expensive but also difficult to be merged into the existing silicon microelectronics industry. Therefore, it would be highly advantageous to grow GaN on silicon substrates due to the potential integration between GaN electronics and silicon technique. Nevertheless, a large density of defects and cracks arising from a 17% lattice mismatch between GaN and Si becomes a major impediment [3–5]. There have been some reports about GaN grown on Si substrates through some particular buffers such as HfN [3] and -SiC (cubic SiC or 3C–SiC) [6,7] for overcoming the large density of defects and cracks. Differently, in our laboratory, a porous -SiC (PSC) buffer layer was fabricated while the purpose of this
∗ Corresponding author. E-mail address: [email protected] (S.-H. Chang). 0924-4247/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2008.03.013
paper is to develop the MSM (metal–semiconductor–metal) photodetector using GaN films grown on Si substrate. The structure is: metal/GaN/PSC/Si(1 1 1) substrate as illustrated in Fig. 1. Furthermore, the photo/dark current ratio (PDCR) of GaN/PSC/Si-MSM photodetector for 366 nm light source under 25 ◦ C operating temperature is reported and compared with that of GaN/-SiC/Si-MSM photodetector. The experimental results show that the properties of the developed GaN/PSC/Si-MSM photodetector are indeed better than that of GaN/-SiC/Si-MSM one. 2. Device fabrications The -SiC films were grown on 1 cm × 1 cm, 500 ± 25 m thickness n-type Si(1 1 1) substrates by a RTCVD (rapid thermal chemical vapor deposition) system. Prior to the -SiC films growth, the substrates were held at 900 ◦ C for 10 min in high vacuum (10−6 Torr) to remove the native oxide layer. After the cooling of substrates to room temperature, the propone (C3 H8 ) was used to carbonize the Si substrate [8]. Again, after the cooling of substrates to room temperature, SiH4 (85 sccm), C3 H8 (60 sccm), and H2 (50 sccm) were introduced into the reaction tube and kept the pressure at 5 mTorr for growing -SiC films. Next, the substrate temperature was increased to 1150 ◦ C rapidly and held for 10 min to deposit the 5880 A˚ thickness of -SiC films. In order to form the porous -SiC, after the deposition of the -SiC films, using the solution of (1HF + 1H2 O + 2C2 H5 OH) to anodize the -SiC/Si under halogen lamp illumination at 50 W for 1–5 min [9]. Sequentially, the GaN was grown on both -SiC/Si and PSC/Si substrates in a Thomas Swan designed metal–organic chemical
2
S.-H. Chang et al. / Sensors and Actuators A 147 (2008) 1–5
Fig. 1. Schematic structure of MSM GaN photodetector on Si(1 1 1) substrate.
vapor deposition (MOCVD) reactor. Firstly, the -SiC/Si and PSC/Si substrates were cleaned and immediately loaded into the reactor. Next, 500 A˚ GaN films was grown at 550 ◦ C following the conditions of 300 Torr for the reactor pressure, 100 rpm for the substrates rotation speed, 10,000 sccm for the flow rate of NH3 gas, 28 sccm for trimethylgallium (TMGa) and 10,000 sccm for carrier gas H2 , ˚ respectively. The growth rate of GaN is about 120 A/min. Then, 2.9 m GaN films were grown on both the -SiC/Si and PSC/Si substrates at 1100 ◦ C with the conditions of 600 Torr for the reactor pressure and 100 rpm for the substrates rotation speed. The flow rate of NH3 gas, TMGa and carrier gas H2 are 12,000, 85 and 10,000 sccm, respectively. The growth rate of GaN is about ˚ 167 A/min. Finally, the Au was evaporated on GaN surface to form the eight-fingers-mask electrodes (Fig. 1) to develop the MSM GaN photodetector. 3. Results and discussions The crystalline structures of -SiC/Si were examined with highresolution X-ray diffractometry (HRXRD) analysis as shown in Fig. 2. The sharp and strong peak located at the diffraction angles 35.7◦ represents for high quality of -SiC (1 1 1), which is in accordance with the report of reference [7]. Fig. 3(a)–(e) shows the SEM photos of the top view of anodized -SiC/Si for 1–5 min, respectively.
From Fig. 3(a), some small but not obvious pits were formed under the etching for 1 min while the porous -SiC were developed under the etching for 2 min as shown in Fig. 3(b) and the inset, the triple scale of Fig. 3(b). In addition, as illustrated in Fig. 3(c), the pits were enlarged and part damaged under the etching for 3 min. Moreover, after the etching for 4 and 5 min as observed in Fig. 3(d) and (e), no pits were fond as well as they revealed electropolishing. Therefore, the anodized -SiC/Si has well porous structure under the etching for 2 min. On the other hand, from the SEM photos in Fig. 4(a) and (b), the top view show the surface morphology of the asdeposited GaN/-SiC/Si is terrible but more uniform and smoother on GaN/PSC/Si. As seen in Fig. 5(a) and (b), the SEM photos of the side view of GaN/PSC/Si and GaN/-SiC/Si, the GaN films grown on PSC/Si are denser and more regular than that on -SiC/Si while the thicknesses of SiC and GaN in Fig. 5(a) and (b) are 498 nm, 588 nm and 2.9 m, 2.91 m, respectively. Both phenomena of Figs. 4 and 5 present the PSC indeed can help better quality GaN thin films grown on Si substrates, causing the PSC can reduce dislocation density [10]. Additionally, the PL system with 325 nm He–Cd pumping laser was used to analyze the undoped GaN/-SiC/Si and GaN/PSC/Si for 1–5 min of etching time of -SiC. As shown in Fig. 6, under the 2 min etching process of -SiC/Si resulting in well porous -SiC (see Fig. 3(b)), one can find the strongest peak located at about 3.4 eV represents the energy gap of h-GaN at 300 K, while the etching times over 3 min result in bad qualities of GaN films grown on PSC/Si and lead low PL intensities. Fig. 7 illustrates the reverse and the forward I–V characters of the GaN/-SiC/Si and GaN/PSC/Si photodetectors under the irradiation of light source, i.e., a UV hand lamp (UVP, UVGL-58) with the wavelength of 366 nm at the power of 6 mW/cm2 . The PDCR (photo/dark current ratio) is calculated with the formula: PDCR =
Fig. 2. XRD profiles in 2/ mode for the undoped -SiC/Si(1 1 1).
Ip − Id Id
(1)
where Id is the dark current, Ip is the photo-current (i.e. the current under illumination). Furthermore, in Fig. 7(a) and (b), the photo and dark currents for GaN/PSC/Si and GaN/-SiC/Si are 0.02013, 0.01693 A and 8.29 × 10−6 , 4.10 × 10−4 A at 1.25 V forward bias, so that the PDCR is 2427.23 and 40.29, respectively. This means the PDCR of GaN/PSC/Si photodetector is about 60 times the value of GaN/-SiC/Si, thus evidenced the PSC indeed can help low leakage
S.-H. Chang et al. / Sensors and Actuators A 147 (2008) 1–5
3
Fig. 3. (a–e) The SEM photos of the top view of anodized -SiC/Si for 1–5 min, respectively. While the inset presents the triple scale of (b).
current GaN thin films grown on Si substrates. It is well known, the dark current is increasing with the dislocation density and the stress between two epitaxial layers. We attribute the lower dark current of GaN/PSC/Si photodetector than that of GaN/-SiC/Si to the less dislocation density and the stress in GaN/PSC/Si [11]. On the
other hand, Chuang et al. [12] recently reported a similar photodetector with very low dark current. The sample structure in [12] is more complicated than ours, so that the good buffer layers between GaN and Si induce less dislocation density and the stress, as well as lead very low dark current. Comparatively, our sample struc-
Fig. 4. (a and b) SEM photos of the top view of the as-deposited GaN/PSC/Si and GaN/-SiC/Si.
4
S.-H. Chang et al. / Sensors and Actuators A 147 (2008) 1–5
Fig. 7. (a) The reverse and the forward I–V characters of the GaN/PSC/Si and GaN/SiC/Si photodetectors. (b) The curves of dark currents with zoom scales of (a). Fig. 5. (a and b) SEM photos of the side view of the as-deposited GaN/PSC/Si and GaN/-SiC/Si.
Fig. 8. Measured responsivity of the GaN/PSC/Si photodetector at a 5 V applied bias.
ture GaN/PSC/Si is simple to make, but the dark current seems to be high. Additionally, from Fig. 8, the measured responsivity at a 5 V applied bias for the GaN/PSC/Si photodetector at = 360 nm is 0.134 A/W which is 28% lower than 0.187 A/W reported in [12]. 4. Conclusion
Fig. 6. Photo-luminescence spectra for the undoped GaN/PSC/Si (etching 2 min) and GaN/-SiC/Si for 1–5 min of etching time of -SiC.
In summary, the GaN MSM photodetectors using GaN films grown on -SiC/Si and porous -SiC/Si have been successfully developed. For GaN/PSC/Si, we found a very high photo/dark current ratio of 2427.23, which is about 60 times the value of GaN/-
S.-H. Chang et al. / Sensors and Actuators A 147 (2008) 1–5
SiC/Si, thus evidenced the PSC indeed can help low leakage current GaN thin films grown on Si substrates. References [1] M. Razeghi, A. Rogalski, Semiconductor ultraviolet detectors, J. Appl. Phys. 79 (10) (1996) 7433–7473. [2] S.J. Pearton, J.C. Zolper, R.J. Shul, F. Ren, GaN: processing, defects and devices, J. Appl. Phys. 86 (1) (1999) 1–78. [3] R. Armitage, Q. Yang, H. Feick, J. Gebauer, E.R. Weber, S. Shinkai, K. Sasaki, Latticematched HfN buffer layers for epitaxy of GaN on Si, Appl. Phys. Lett. 81 (8) (2002) 1450–1452. [4] M. Seon, T. Prokofyeva, M. Holtz, S.A. Nikishin, N.N. Faleev, H. Temkin, Selective growth of high quality GaN on Si(1 1 1) substrates, Appl. Phys. Lett. 76 (14) (2000) 1842–1844. [5] D. Wang, Y. Hiroyama, M. Tamura, M. Ichikawa, S. Yoshida, Growth of hexagonal GaN on Si(1 1 1) coated with a thin flat SiC buffer layer, Appl. Phys. Lett. 77 (12) (2000) 1846. [6] J. Wu, H. Yaguchi, H. Nagasawa, Y. Yamaguchi, K. Onabe, Y. Shiraki, R. Ito, Investigation of luminescence properties of GaN single crystals grown on 3C–SiC substrates, J. Crys. Grow. 189/190 (1998) 420–424. [7] C.I. Park, J.H. Kang, K.C. Kim, K.S. Nahm, E.-K. Suh, K.Y. Lim, Metal–organic chemical vapor deposition growth of GaN thin film on 3C–SiC/Si(1 1 1) substrate using various buffer layers, Thin Solid Films 401 (2001) 60–66.
5
[8] M.I. Chaudhry, Electrical transport properties of crystalline silicon carbide/silicon heterojunctions, IEEE Electron Device Lett. 12 (1991) 670–672. [9] Akira Takazawa, Tetsuro Tamura and Masao Yamada, Porous -SiC fabrication by electrochemical anodization, Jpn. J. Appl. Phys., Vol. 32, pp. 3148–3149, Part 1, No. 7, July, 1993. [10] C.K. Inoki, T.S. Kuan, A. Sagar, C.D. Lee, R.M. Feenstra, D.D. Koleske, D.J. Diaz, P.W. Bohn, I. Adesida, Growth of GaN on porous SiC and GaN substrates, Physica Status Solidi (a) 200 (1) (2003) 44–47. [11] A. Sagar, C.D. Lee, R.M. Feenstra, C.K. Inoki, T.S. Kuan, Plasma-assisted molecular beam epitaxy of GaN on porous SiC substrates with varying porosity, J. Vacu. Sci. & Tech. B: Microelectronics and Nanometer Structures 21 (2003) 1812–1817. [12] R.W. Chuang, S.P. Chang, S.J. Chang, Y.Z. Chiou, C.Y. Lu, T.K. Lin, Y.C. Lin, C.F. Kuo, H.M. Chang, Gallium Nitride metal–semiconductor–metal photodetectors prepared on silicon substrates, J. Appl. Phys. 102 (2007) 073110.
Biography Shiuan-Ho Chang born in Taipei, Taiwan, Feb., 1971. He graduated from the “Institute of Microelectronics, Department of Electrical Engineering, National Cheng Kung University”, Tainan, Taiwan, and now he is an assistant professor in Department of Computer and Communication, Diwan University, Madou Town, Tainan, 721, Taiwan.
Contents lists available at ScienceDirect
Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna
GaN UV MSM photodetector on porous -SiC/(1 1 1)Si substrates Shiuan-Ho Chang a,∗ , Yean-Kuen Fang b , Kai-Chun Hsu b , Tzu-Chieh Wei b a b
Department of Computer and Communication, Diwan University, Madou Town, Tainan 721, Taiwan VLSI Technology Laboratory, Institute of Microelectronics, Department of Electrical Engineering, National Cheng Kung University, Tainan, Taiwan
a r t i c l e
i n f o
Article history: Received 22 December 2007 Received in revised form 22 February 2008 Accepted 11 March 2008 Available online 20 March 2008 Keywords: GaN Porous -SiC MSM
a b s t r a c t This paper reports the GaN thin films grown on Si substrates by MOCVD with different buffer layers, i.e., cubic -SiC and porous -SiC (PSC). The -SiC thin films were prepared with RTCVD, while the PSC thin films were fabricated by electrochemical anodization method on cubic -SiC thin films, as well as the PL spectrometer, HRXRD and SEM were employed to analyze the samples. Furthermore, a metal–semiconductor–metal (MSM) photodetectors using GaN films grown on -SiC/Si and porous -SiC/Si were developed. For GaN/PSC/Si, we found a very high photo/dark current ratio of 2427.23, which is about 60 times the value of GaN/-SiC/Si, thus evidenced the PSC indeed can help low leakage current and high-quality GaN thin films grown on Si substrates. © 2008 Elsevier B.V. All rights reserved.
1. Introduction It is necessary to develop ultraviolet (UV) detectors for sensing rapidly mature InGaN LEDs and laser, causing the UV detectors have been employed for flame monitoring, pollution analyzers, UV astronomy, and medical instruments [1]. Recently, there are great investigations of electronics and optoelectronics based on the group III nitride material systems for their high thermal conductivity, robust chemical bonding, high breakdown field strength and the established hetero-structure epitaxy technologies [2]. In the group III nitride materials system, GaN is one of the most important wide band gap semiconductor due to its numerous applications in ultraviolet-blue optical devices. However, GaN is generally grown on sapphire or silicon carbide substrates, which are not only expensive but also difficult to be merged into the existing silicon microelectronics industry. Therefore, it would be highly advantageous to grow GaN on silicon substrates due to the potential integration between GaN electronics and silicon technique. Nevertheless, a large density of defects and cracks arising from a 17% lattice mismatch between GaN and Si becomes a major impediment [3–5]. There have been some reports about GaN grown on Si substrates through some particular buffers such as HfN [3] and -SiC (cubic SiC or 3C–SiC) [6,7] for overcoming the large density of defects and cracks. Differently, in our laboratory, a porous -SiC (PSC) buffer layer was fabricated while the purpose of this
∗ Corresponding author. E-mail address: [email protected] (S.-H. Chang). 0924-4247/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2008.03.013
paper is to develop the MSM (metal–semiconductor–metal) photodetector using GaN films grown on Si substrate. The structure is: metal/GaN/PSC/Si(1 1 1) substrate as illustrated in Fig. 1. Furthermore, the photo/dark current ratio (PDCR) of GaN/PSC/Si-MSM photodetector for 366 nm light source under 25 ◦ C operating temperature is reported and compared with that of GaN/-SiC/Si-MSM photodetector. The experimental results show that the properties of the developed GaN/PSC/Si-MSM photodetector are indeed better than that of GaN/-SiC/Si-MSM one. 2. Device fabrications The -SiC films were grown on 1 cm × 1 cm, 500 ± 25 m thickness n-type Si(1 1 1) substrates by a RTCVD (rapid thermal chemical vapor deposition) system. Prior to the -SiC films growth, the substrates were held at 900 ◦ C for 10 min in high vacuum (10−6 Torr) to remove the native oxide layer. After the cooling of substrates to room temperature, the propone (C3 H8 ) was used to carbonize the Si substrate [8]. Again, after the cooling of substrates to room temperature, SiH4 (85 sccm), C3 H8 (60 sccm), and H2 (50 sccm) were introduced into the reaction tube and kept the pressure at 5 mTorr for growing -SiC films. Next, the substrate temperature was increased to 1150 ◦ C rapidly and held for 10 min to deposit the 5880 A˚ thickness of -SiC films. In order to form the porous -SiC, after the deposition of the -SiC films, using the solution of (1HF + 1H2 O + 2C2 H5 OH) to anodize the -SiC/Si under halogen lamp illumination at 50 W for 1–5 min [9]. Sequentially, the GaN was grown on both -SiC/Si and PSC/Si substrates in a Thomas Swan designed metal–organic chemical
2
S.-H. Chang et al. / Sensors and Actuators A 147 (2008) 1–5
Fig. 1. Schematic structure of MSM GaN photodetector on Si(1 1 1) substrate.
vapor deposition (MOCVD) reactor. Firstly, the -SiC/Si and PSC/Si substrates were cleaned and immediately loaded into the reactor. Next, 500 A˚ GaN films was grown at 550 ◦ C following the conditions of 300 Torr for the reactor pressure, 100 rpm for the substrates rotation speed, 10,000 sccm for the flow rate of NH3 gas, 28 sccm for trimethylgallium (TMGa) and 10,000 sccm for carrier gas H2 , ˚ respectively. The growth rate of GaN is about 120 A/min. Then, 2.9 m GaN films were grown on both the -SiC/Si and PSC/Si substrates at 1100 ◦ C with the conditions of 600 Torr for the reactor pressure and 100 rpm for the substrates rotation speed. The flow rate of NH3 gas, TMGa and carrier gas H2 are 12,000, 85 and 10,000 sccm, respectively. The growth rate of GaN is about ˚ 167 A/min. Finally, the Au was evaporated on GaN surface to form the eight-fingers-mask electrodes (Fig. 1) to develop the MSM GaN photodetector. 3. Results and discussions The crystalline structures of -SiC/Si were examined with highresolution X-ray diffractometry (HRXRD) analysis as shown in Fig. 2. The sharp and strong peak located at the diffraction angles 35.7◦ represents for high quality of -SiC (1 1 1), which is in accordance with the report of reference [7]. Fig. 3(a)–(e) shows the SEM photos of the top view of anodized -SiC/Si for 1–5 min, respectively.
From Fig. 3(a), some small but not obvious pits were formed under the etching for 1 min while the porous -SiC were developed under the etching for 2 min as shown in Fig. 3(b) and the inset, the triple scale of Fig. 3(b). In addition, as illustrated in Fig. 3(c), the pits were enlarged and part damaged under the etching for 3 min. Moreover, after the etching for 4 and 5 min as observed in Fig. 3(d) and (e), no pits were fond as well as they revealed electropolishing. Therefore, the anodized -SiC/Si has well porous structure under the etching for 2 min. On the other hand, from the SEM photos in Fig. 4(a) and (b), the top view show the surface morphology of the asdeposited GaN/-SiC/Si is terrible but more uniform and smoother on GaN/PSC/Si. As seen in Fig. 5(a) and (b), the SEM photos of the side view of GaN/PSC/Si and GaN/-SiC/Si, the GaN films grown on PSC/Si are denser and more regular than that on -SiC/Si while the thicknesses of SiC and GaN in Fig. 5(a) and (b) are 498 nm, 588 nm and 2.9 m, 2.91 m, respectively. Both phenomena of Figs. 4 and 5 present the PSC indeed can help better quality GaN thin films grown on Si substrates, causing the PSC can reduce dislocation density [10]. Additionally, the PL system with 325 nm He–Cd pumping laser was used to analyze the undoped GaN/-SiC/Si and GaN/PSC/Si for 1–5 min of etching time of -SiC. As shown in Fig. 6, under the 2 min etching process of -SiC/Si resulting in well porous -SiC (see Fig. 3(b)), one can find the strongest peak located at about 3.4 eV represents the energy gap of h-GaN at 300 K, while the etching times over 3 min result in bad qualities of GaN films grown on PSC/Si and lead low PL intensities. Fig. 7 illustrates the reverse and the forward I–V characters of the GaN/-SiC/Si and GaN/PSC/Si photodetectors under the irradiation of light source, i.e., a UV hand lamp (UVP, UVGL-58) with the wavelength of 366 nm at the power of 6 mW/cm2 . The PDCR (photo/dark current ratio) is calculated with the formula: PDCR =
Fig. 2. XRD profiles in 2/ mode for the undoped -SiC/Si(1 1 1).
Ip − Id Id
(1)
where Id is the dark current, Ip is the photo-current (i.e. the current under illumination). Furthermore, in Fig. 7(a) and (b), the photo and dark currents for GaN/PSC/Si and GaN/-SiC/Si are 0.02013, 0.01693 A and 8.29 × 10−6 , 4.10 × 10−4 A at 1.25 V forward bias, so that the PDCR is 2427.23 and 40.29, respectively. This means the PDCR of GaN/PSC/Si photodetector is about 60 times the value of GaN/-SiC/Si, thus evidenced the PSC indeed can help low leakage
S.-H. Chang et al. / Sensors and Actuators A 147 (2008) 1–5
3
Fig. 3. (a–e) The SEM photos of the top view of anodized -SiC/Si for 1–5 min, respectively. While the inset presents the triple scale of (b).
current GaN thin films grown on Si substrates. It is well known, the dark current is increasing with the dislocation density and the stress between two epitaxial layers. We attribute the lower dark current of GaN/PSC/Si photodetector than that of GaN/-SiC/Si to the less dislocation density and the stress in GaN/PSC/Si [11]. On the
other hand, Chuang et al. [12] recently reported a similar photodetector with very low dark current. The sample structure in [12] is more complicated than ours, so that the good buffer layers between GaN and Si induce less dislocation density and the stress, as well as lead very low dark current. Comparatively, our sample struc-
Fig. 4. (a and b) SEM photos of the top view of the as-deposited GaN/PSC/Si and GaN/-SiC/Si.
4
S.-H. Chang et al. / Sensors and Actuators A 147 (2008) 1–5
Fig. 7. (a) The reverse and the forward I–V characters of the GaN/PSC/Si and GaN/SiC/Si photodetectors. (b) The curves of dark currents with zoom scales of (a). Fig. 5. (a and b) SEM photos of the side view of the as-deposited GaN/PSC/Si and GaN/-SiC/Si.
Fig. 8. Measured responsivity of the GaN/PSC/Si photodetector at a 5 V applied bias.
ture GaN/PSC/Si is simple to make, but the dark current seems to be high. Additionally, from Fig. 8, the measured responsivity at a 5 V applied bias for the GaN/PSC/Si photodetector at = 360 nm is 0.134 A/W which is 28% lower than 0.187 A/W reported in [12]. 4. Conclusion
Fig. 6. Photo-luminescence spectra for the undoped GaN/PSC/Si (etching 2 min) and GaN/-SiC/Si for 1–5 min of etching time of -SiC.
In summary, the GaN MSM photodetectors using GaN films grown on -SiC/Si and porous -SiC/Si have been successfully developed. For GaN/PSC/Si, we found a very high photo/dark current ratio of 2427.23, which is about 60 times the value of GaN/-
S.-H. Chang et al. / Sensors and Actuators A 147 (2008) 1–5
SiC/Si, thus evidenced the PSC indeed can help low leakage current GaN thin films grown on Si substrates. References [1] M. Razeghi, A. Rogalski, Semiconductor ultraviolet detectors, J. Appl. Phys. 79 (10) (1996) 7433–7473. [2] S.J. Pearton, J.C. Zolper, R.J. Shul, F. Ren, GaN: processing, defects and devices, J. Appl. Phys. 86 (1) (1999) 1–78. [3] R. Armitage, Q. Yang, H. Feick, J. Gebauer, E.R. Weber, S. Shinkai, K. Sasaki, Latticematched HfN buffer layers for epitaxy of GaN on Si, Appl. Phys. Lett. 81 (8) (2002) 1450–1452. [4] M. Seon, T. Prokofyeva, M. Holtz, S.A. Nikishin, N.N. Faleev, H. Temkin, Selective growth of high quality GaN on Si(1 1 1) substrates, Appl. Phys. Lett. 76 (14) (2000) 1842–1844. [5] D. Wang, Y. Hiroyama, M. Tamura, M. Ichikawa, S. Yoshida, Growth of hexagonal GaN on Si(1 1 1) coated with a thin flat SiC buffer layer, Appl. Phys. Lett. 77 (12) (2000) 1846. [6] J. Wu, H. Yaguchi, H. Nagasawa, Y. Yamaguchi, K. Onabe, Y. Shiraki, R. Ito, Investigation of luminescence properties of GaN single crystals grown on 3C–SiC substrates, J. Crys. Grow. 189/190 (1998) 420–424. [7] C.I. Park, J.H. Kang, K.C. Kim, K.S. Nahm, E.-K. Suh, K.Y. Lim, Metal–organic chemical vapor deposition growth of GaN thin film on 3C–SiC/Si(1 1 1) substrate using various buffer layers, Thin Solid Films 401 (2001) 60–66.
5
[8] M.I. Chaudhry, Electrical transport properties of crystalline silicon carbide/silicon heterojunctions, IEEE Electron Device Lett. 12 (1991) 670–672. [9] Akira Takazawa, Tetsuro Tamura and Masao Yamada, Porous -SiC fabrication by electrochemical anodization, Jpn. J. Appl. Phys., Vol. 32, pp. 3148–3149, Part 1, No. 7, July, 1993. [10] C.K. Inoki, T.S. Kuan, A. Sagar, C.D. Lee, R.M. Feenstra, D.D. Koleske, D.J. Diaz, P.W. Bohn, I. Adesida, Growth of GaN on porous SiC and GaN substrates, Physica Status Solidi (a) 200 (1) (2003) 44–47. [11] A. Sagar, C.D. Lee, R.M. Feenstra, C.K. Inoki, T.S. Kuan, Plasma-assisted molecular beam epitaxy of GaN on porous SiC substrates with varying porosity, J. Vacu. Sci. & Tech. B: Microelectronics and Nanometer Structures 21 (2003) 1812–1817. [12] R.W. Chuang, S.P. Chang, S.J. Chang, Y.Z. Chiou, C.Y. Lu, T.K. Lin, Y.C. Lin, C.F. Kuo, H.M. Chang, Gallium Nitride metal–semiconductor–metal photodetectors prepared on silicon substrates, J. Appl. Phys. 102 (2007) 073110.
Biography Shiuan-Ho Chang born in Taipei, Taiwan, Feb., 1971. He graduated from the “Institute of Microelectronics, Department of Electrical Engineering, National Cheng Kung University”, Tainan, Taiwan, and now he is an assistant professor in Department of Computer and Communication, Diwan University, Madou Town, Tainan, 721, Taiwan.