Transport and infrared photoresponse properties of InN nanorods/Si heterojunction
© Kumar et al; licensee Springer. 2011
Received: 20 April 2011
Accepted: 28 November 2011
Published: 28 November 2011
The present work explores the electrical transport and infrared (IR) photoresponse properties of InN nanorods (NRs)/n-Si heterojunction grown by plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN NRs is verified by the X-ray diffraction and transmission electron microscopy. Raman measurements show that these wurtzite InN NRs have sharp peaks E 2(high) at 490.2 cm-1 and A 1(LO) at 591 cm-1. The current transport mechanism of the NRs is limited by three types of mechanisms depending on applied bias voltages. The electrical transport properties of the device were studied in the range of 80 to 450 K. The faster rise and decay time indicate that the InN NRs/n-Si heterojunction is highly sensitive to IR light.
Semiconducting group-III nitrides have attracted a lot of attention in recent years because of, mainly, the large band gap (0.7 to 6.2 eV) that can be covered by the nitrides and their alloys. Their optical properties are highly suitable for novel optoelectronic and photonic applications. Compared to all other group-III nitrides, InN possesses the lowest effective mass, the highest mobility, narrow band gap E g of 0.7 to 0.9 eV, and the highest saturation velocity [1, 2]. These properties make it an attractive material for applications in solar cells and in terahertz emitters and detectors [3–5]. InN/Si tandem cells have been proposed for high-efficiency solar cells . InN nanostructures can also be used as sensor materials for various gases and liquids . Good-quality InN layers are difficult to grow because of the low dissociation energy of InN and the lack of an appropriate substrates [8, 9]. The above constraints lead to the formation of dislocations and strain in the grown epitaxial layers resulting in the degradation of the device performance. Grandal et al.  reported that defect- and strain-free InN nanostructures of very high crystal quality can be grown by molecular beam epitaxy on silicon substrates.
Due to the distinctive properties and potential applications of nanostructures, various kinds of InN nanostructures have been grown such as nanowires (NWs), nanotubes, and nanorods (NRs) by plasma-assisted molecular beam epitaxy (PAMBE) and metalorganic vapor phase epitaxy [11, 12]. There are several reports on the growth of InN NWs or NRs on Si substrates [13, 14] and few reports on electrical transport [15, 16] but no report on infrared (IR) on/off characteristics of InN nanorods/Si heterojunction. Since silicon is a low-cost and the most sought semiconductor material, it is very important to understand the temperature-dependent transport and IR photoresponse mechanism of InN NRs/Si heterostructure prior to their adoption in the fabrication of optoelectronic device. In the present study, catalyst-free InN NRs were grown on Si substrates by PAMBE and studied the temperature-dependent transport and IR photoresponse mechanism of InN NRs/Si heterostructures.
The InN NRs were grown on n-Si (1 1 1) substrates by PAMBE system. The substrates were chemically cleaned followed by dipping in 5% HF to remove the surface oxide and thermally cleaned at 900°C for an hour in ultra-high vacuum. The substrates were exposed to the Indium (In) molecular beam at 350°C for 60 s (approximately two monolayers). Further, the substrate temperature was increased to 500°C to fabricate the NRs. The duration of NR growth was kept for 2 h. The general set of growth conditions includes indium beam equivalent pressure, nitrogen flow rate, and rf-plasma power, which were kept at 4.6 × 10-8 mbar, 1 SCCM, and 400 W, respectively. The morphological and structural evaluation of the as-grown NRs was carried out by the field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Further, the crystalline quality and lattice structure of the InN NRs were characterized by micro-Raman spectroscopy using a 514-nm line of the Ar+ ion laser at room temperature. The aluminum circular contacts of diameter 400 μm were fabricated by thermal evaporation using a physical mask. The adequate ohmic nature of the contacts to InN and Si was verified. The device transport characteristics were studied at various temperatures using the probe station attached with the KEITHLEY-236 source measure unit (Bell Electronics, Kent, WA, USA), and IR photoresponse characteristics were studied under IR source with 1, 500-nm-long pass filter.
Results and discussion
From Figure 7b, it can be seen that the barrier height (ϕ b) and the ideality factor (η) are dependent on the temperature and are attributed to the inhomogeneity at the interface . The large observed ideality factor suggests the presence of surface or interface states, indicating that the junction is far from being ideal [25, 26]. The large mismatch in the lattice parameters of InN and Si shows that there is generally a high density of interfacial states between two materials. The lattice mismatch produces a dislocation field at the junction interface that can attract a space charge and/or act as a recombination center, resulting in large ideality factor. Breitenstein et al.  introduced a model to describe ideality factors n > 2, which is based on coupled defects and donor acceptor pair recombination, both giving rise to an increased recombination current. It is stated that for a high density of defect states, hopping conduction in the defect volume may govern the reverse conductivity of the devices.
InN NRs/n-Si heterojunction was grown by PAMBE. Single-crystalline wurtzite structure of InN NRs is verified by the X-ray diffraction and HRTEM. Raman spectrum reveals two clear peaks, which correspond to the E 2(high) and A 1(LO) modes of wurtzite InN, respectively. The current transport mechanism of the NRs/Si heterojunctions were limited by three types of mechanisms depending on applied bias voltages. The observed higher value of ideality factor is probably due to the presence of defect states in InN NRs. The rapid rise and decay of infrared on/off characteristics of InN nanorods/Si heterojunction indicate that the device is highly sensitive to the IR light. The InN NRs/Si heterojunction device can be used for IR detectors.
The authors thank the Institute Nanoscience Initiative, IISc for providing the transmission electronic microscopy characterizations.
- Wu J, Walukiewicz W, Yu KM, Ager JW III, Haller EE, Lu H, Schaff WJ, Saito Y, Nanishi Y: Unusual properties of the fundamental band gap of InN. Appl Phys Lett 2002, 80: 3967. 10.1063/1.1482786View Article
- Goiran M, Millot M, Poumirol JM, Gherasoiu I, Walukiewicz W, Leotin J: Electron cyclotron effective mass in indium nitride. Appl Phys Lett 2010, 96: 052117. 10.1063/1.3304169View Article
- Yang HC, Kuo PF, Lin TY, Chen YF, Chen KH, Chen LC, Chyi JI: Mechanism of luminescence in InGaN/GaN multiple quantum wells. Appl Phys Lett 2000, 76: 3712. 10.1063/1.126758View Article
- Bellotti E, Doshi BK, Brennan KF, Albrecht JD, Ruden PP: Ensemble Monte Carlo study of electron transport in wurtzite InN. J Appl Phys 1999, 85: 916. 10.1063/1.369211View Article
- Chang CY, Chi GC, Wang WM, Chen LC, Chen KH, Ren F, Pearton SJ: Transport properties of InN nanowires. Appl Phys Lett 2005, 87: 093112. 10.1063/1.2037850View Article
- Bhuiyan AG, Hashimoto A, Yamamoto A, Indium nitride (InN): A review on growth, characterization, and properties. J Appl Phys 2003, 94: 2779. 10.1063/1.1595135View Article
- Lu H, Schaff WJ, Eastman LF: Surface chemical modification of InN for sensor applications. J Appl Phys 2004, 96: 3577. 10.1063/1.1767608View Article
- Guo Q, Kato O, Yoshida A: Thermal stability of indium nitride single crystal films. J Appl Phys 1993, 73: 7969. 10.1063/1.353906View Article
- Wang K, Reeber RR: Thermal expansion and elastic properties of InN. Appl Phys Lett 2001, 79: 1602. 10.1063/1.1400082View Article
- Grandal J, Sánchez-García MA, Calleja E, Luna E, Trampert A: Accommodation mechanism of InN nanocolumns grown on Si(111) substrates by molecular beam epitaxy. Appl Phys Lett 2007, 91: 021902. 10.1063/1.2756293View Article
- Yun SH, Ra YH, Lee YM, Song KY, Cha JH, Lim HC, Kim DW, Kissinger NJS, Lee CR: Growth of hexagonal and cubic InN nanowires using MOCVD with different growth temperatures. J Cryst Growth 2010, 312: 2201. 10.1016/j.jcrysgro.2010.04.041View Article
- Stoica T, Meijers RJ, Calarco R, Richter T, Sutter E, Lüth H: Photoluminescence and intrinsic properties of MBE-grown InN nanowires. Nano Lett 2006, 6: 1541. 10.1021/nl060547xView Article
- Wu J: When group-III nitrides go infrared: new properties and perspectives. J Appl Phys 2009, 106: 011101. 10.1063/1.3155798View Article
- Shen CH, Chen HY, Lin HW, Gwo S, Klochikhin AA, Davydov VY: Near-infrared photoluminescence from vertical InN nanorod arrays grown on silicon: effects of surface electron accumulation layer. Appl Phys Lett 2006, 88: 253104. 10.1063/1.2216924View Article
- Werner F, Limbach F, Carsten M, Denker C, Malindretos J, Rizzi A: Electrical conductivity of InN nanowires and the influence of the native indium oxide formed at their surface. Nano Lett 2009, 9: 1567. 10.1021/nl8036799View Article
- Calleja E, Grandal J, Sánchez-García MA, Niebelschütz M, Cimalla V, Ambacher O: Evidence of electron accumulation at nonpolar surfaces of InN nanocolumns. Appl Phys Lett 2007, 90: 262110. 10.1063/1.2749871View Article
- Chao CK, Chyi JI, Hsiao CN, Kei CC, Kuo SY, Chang HS, Hsu TM: Catalyst-free growth of indium nitride nanorods by chemical-beam epitaxy. Appl Phys Lett 2006, 88: 233111. 10.1063/1.2210296View Article
- Pu XD, Chen J, Shen WZ, Ogawa H, Guo QX: Temperature dependence of Raman scattering in hexagonal indium nitride films. J Appl Phys 2005, 98: 033527. 10.1063/1.2006208View Article
- Wang X, Che S, Ishitani Y, Yoshikawa A: Experimental determination of strain-free Raman frequencies and deformation potentials for the E 2 (high) and A 1 (LO) modes in hexagonal InN. Appl Phys Lett 2005, 89: 171907.View Article
- Yoshimoto M, Yamamoto Y, Saraie J: Fabrication of InN/Si heterojunctions with rectifying characteristics. Phys Stat Sol (C) 2003, 0/7: 2794.View Article
- Huang Y, Chen XD, Fung S, Beling CD, Ling CC, Dai XQ, Xie MH: Current transport property of n -GaN/ n -6H-SiC heterojunction: influence of interface states. Appl Phys Lett 2005, 86: 122102. 10.1063/1.1886906View Article
- Kribes Y, Harrieon I, Tuck B, Cheng TS, Foxon CT: Electrical properties of n-GaN/n + -GaAs interfaces. J Cryst Growth 1998, 189/190: 773. 10.1016/S0022-0248(98)00289-9View Article
- Ghosh R, Basak D: Electrical and ultraviolet photoresponse properties of quasialigned ZnO nanowires/ p -Si heterojunction. Appl Phys Lett 2007, 90: 243106. 10.1063/1.2748333View Article
- Iucolano F, Roccaforte F, Giannazzo F, Raineri V: Barrier inhomogeneity and electrical properties of Pt/GaN Schottky contacts. J Appl Phys 2007, 102: 113701. 10.1063/1.2817647View Article
- Lao CS, Liu J, Gao P, Zhang L, Davidovic D, Tummala R, Wang ZL: ZnO nanobelt/nanowire Schottky diodes formed by dielectrophoresis alignment across au electrodes. Nano Lett 2006, 6: 263. 10.1021/nl052239pView Article
- Brotzmann M, Vetter U, Hofsass H: BN/ZnO heterojunction diodes with apparently giant ideality factors. J Appl Phys 2009, 106: 063704. 10.1063/1.3212987View Article
- Breitenstein O, Altermatt P, Ramspeck K, Schenk A: The origin of ideality factors n > 2 of shunts and surfaces in the dark I-V curves of Si solar cells. In Proceedings of the 21st European Photovoltaic Solar Energy Conference. Munich: WIP; 2006:625–628.
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