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研究生： 黃鋒文
Huang, Feng-Wen
論文名稱： 氮化鎵系列摻雜錳之材料特性與元件應用
Characterization of Mn-doped GaN-based material and device application
指導教授： 許進恭
Sheu, Jinn-Kong
學位類別： 博士
Doctor
系所名稱： 理學院 - 光電科學與工程學系
Department of Photonics
論文出版年： 2012
畢業學年度： 100
語文別： 英文
論文頁數： 183
中文關鍵詞： 有機金屬氣相磊晶法 、氮化鎵摻雜錳 、光子能量向上轉換 、中間能帶 、太陽能電池 、錳殘留效應 、氮化銦鎵摻雜錳
外文關鍵詞： Mn-doped GaN, memory effect, up-converter, intermediate band solar cell, spintronics, MOVPE
相關次數： 點閱：130  下載：0 
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    • 本論文以有機金屬氣相磊晶法成長氮化鎵摻雜錳系列材料，並研究其材料特性與元件應用。

    材料分析方面，我們研究材料之表面形貌、結晶品質、光學特性、電傳輸特性、磁性、電子束縛能與相對外部量子效率(光響應特性)。元件應用方面，由於氮化鎵摻雜錳之材料具有中間能帶的特性，我們已成功利用此特性而設計出可將光子能量向上轉換的元件系統以及中間能帶型結構之太陽能電池。

    材料成長方面，我們發現錳原子具有腔體殘留效應，並且存在表面偏析與再擴散的現象。我們亦發現若先將受到錳污染的腔體曝於大氣環境一段時間後再將腔體進行氫氣氛圍之高溫清潔則可以有效地消除錳殘留效應。此外，我們亦發現若先使用鹽酸將試片表面加以清洗則可以有效地去除部份的錳偏析。除此之外，我們亦發現若將錳摻雜於氮化銦鎵材料中，銦原子與錳原子的併入具有競爭的關係。

    元件應用方面，我們成功地利用氮化鎵摻雜錳材料之中間能帶的性質搭配多重量子井的結構而設計出可將光子能量向上轉換的元件系統。其中氮化鎵摻雜錳材料扮演低能量光子的吸收層，而多重量子井結構則扮演高能量光子的發射層。我們藉由變功率的螢光光譜與光電流頻譜推測可能的發光機制，其發光來源可能來自於光激載子的注入。在沒有外加偏壓的條件下，光子向上轉換的能量約為450 meV。

    另外一方面，我們亦成功地製作出以氮化鎵摻雜錳材料為吸收層之中間能帶型結構的太陽能電池。我們藉由穿透光譜與相對外部量子效率頻譜的量測證實了中間能帶的吸收特性，此太陽能電池展現出符合預期之高短路電流增幅的元件特性。此外，我們亦利用雙光源激發系統搭配鎖相放大技術證實了此元件的確具有雙光子吸收(中間能帶跳躍機制)的特性。

    最後我們初步地成長以氮化銦鎵摻雜錳材料為吸收層之中間能帶型結構的太陽能電池，雖然元件具有中間能帶的吸收特性，然而此元件並未展現出如預期之高短路電流增幅的特性。其光電流下降的主要原因推測為過低的材料品質與過高的串聯電阻效應以及光子選擇性的問題，未來我們可嘗試藉由侷限光子的設計以及高厚度的主動層來克服光子選擇性的問題。

    In present dissertation, characterization of Mn-doped GaN-based material and device application grown by metalorganic vapor phase epitaxy (MOVPE) were investigated. The surface morphology, crystallinity, optical, electrical, magnetic properties, electron binding energy and relative external quantum efficiency (photo-response) of Mn-doped GaN-based material and devices were studied.
    The memory effect and redistribution of manganese (Mn) into subsequently regrown GaN-based epitaxial layers by metalorganic vapor phase epitaxy were revealed. Low-temperature up-converted photoluminescence (UPL) and the secondary ion mass spectrometry were performed on GaN-based epitaxial samples with and without Mn doping to study the effect of residual Mn on optical property. UPL emission, which originated from residual Mn doping in regrown InGaN quantum wells (QWs) because of the memory effect of the reactor, could be eliminated in an air-exposed and H2-baking manner prior to the regrowth of the QWs. Considerable residual Mn background level and slow decay rate of Mn concentration tail were also observed in the regrown epitaxial layers, which could be attributed to the memory effect or surface segregation and diffusion from the Mn-doped underlying layer during regrowth in the Mn-free reactor. The surface segregation of Mn on the Mn-doped layer could be partially removed by hydrogen chloride-etched treatment. Competition between Mn and In atoms during the growth of InGaN material was also addressed in the current study.
    An up-conversion phenomenon was observed due to the Mn doping effect in the GaN-based material. Here, we further investigated the possible mechanism of the up-converted photoluminescence. Up-converted heterostructures with a Mn-doped underlying GaN intermediate band photodetection layer and an InGaN/GaN multiple quantum wells (MQWs) luminescence layer grown by metal-organic vapor-phase epitaxy were demonstrated. The up-converters exhibited a significant up-converted photoluminescence (UPL) signal. Power-dependent UPL and spectral responses indicated that the UPL emission could be due to photo-carrier injection from the Mn-doped GaN layer into InGaN/GaN MQWs. Photons convert from 2.54 to 2.99 eV via a single-photon absorption process to exhibit linear up-conversion photon energy of ~450 meV without applying bias voltage. Therefore, the up-conversion process could be interpreted within the uncomplicated energy-levels model.
    Intermediate band (IB) p-i-n solar cells with Mn-doped GaN absorption layer grown by metal-organic vapor-phase epitaxy were presented. The measurements of transmittance spectrum and relative external quantum efficiency (EQE) showed the presence of an IB absorption property. The IB devices showed additional infrared-visible-light region response and could be promising in high-efficiency solar cell applications. A large enhancement in short circuit current-density and a slight decrease in open circuit voltage were observed. The increased photocurrent of the cells without too much voltage reduction was a key point for IB operation. Power-dependent dual-light source excitation and lock-in amplifier techniques were performed to prove that “two-photon absorption process” actually takes place in IB solar cells with Mn-doped GaN absorption layer. Mn-doped InxGa1-xN material showed potential in high-efficiency solar cell applications by its effective usage in IB photovoltaic devices.
    Furthermore, the intermediate band solar cells with Mn-doped In0.084Ga0.916N absorption layer were presented initially. The efficiency was decreased due to the decrease of the Voc, Jsc and FF. The decreased efficiency could be attributed to the poor quality of Mn-doped InGaN material and the photon selectivity issue. The decreased Jsc was attributed to the decreased photocurrent due to the large non-radiative recombination associated with the poor quality, the photon selectivity issue and the high series resistance of Mn-doped InGaN even though the devices exhibited the additional absorption of the photons with energy below the VB-CB bandgap. Furthermore, the material quality of InGaN should be improved and the absorption of photon selectivity issue should be considered. The using of light confinement and the large thickness of Mn-doped InGaN would be necessary to efficiently absorb the lower energy photons with the weak absorption coefficient for the realization of IB photovoltaic devices. In addition to the issues of Jsc and Voc, obtaining a high FF for improving cell efficiency was also a key point. Therefore, attention should be focused on the reduction of series resistance to improve conversion efficiency by incorporation IB into the absorption layer of solar cells.

    Contents 摘要(Abstract in Chinese) I Abstract II 誌謝(Acknowledgement) IV Contents V Figure Captions VII Chapter 1 Introduction 1 1.1 AlGaInN Material for Photovoltaic Device Absorbing Full Solar Spectra 1 1.2 Intermediate Band Solar Cell 2 1.3 Up/down-converter and Solar Cell 5 1.4 Spintronics 8 References in Chapter 1 11 Chapter 2 Physics 19 2.1 Fundamentals of Solar Cell 19 2.1.1 Physical Basis of Photovoltaics Operation 19 2.1.2 Light Absorption and Generation Rate 20 2.1.3 Recombination and Carrier Transport 26 2.1.4 Solar Cell I-V Characteristics and Parasitic Resistance Effects 32 2.1.5 Spectral Response, Efficiency and Band Gap 37 2.2 Theoretical Conversion Limits of Intermediate Band Solar Cell 39 2.2.1 The Shockley and Queisser (SQ) Limits of a Photovoltaic Converter 39 2.2.2 Intermediate Band Solar Cell 42 2.3 Theoretical Conversion Limits of Up/down-conversion Solar Cell 48 References in Chapter 2 51 Chapter 3 Characterization of Mn-doped GaN-based Material Grown by Metal-Organic Vapor-Phase Epitaxy 53 3.1 Growth and Doping-control Technology 53 3.1.1 Bubbler and Manganese Source 53 3.1.2 Incorporation of Metal-organic Precursor and Molar Flow Rate 55 3.1.3 Effect of Epitaxial Parameters on Incorporation Efficiency of Mn Dopant in GaN 57 3.2 Surface Morphology and Crystallinity 62 3.3 Optoelectronic, Magnetic Property and Effect of Mn-doping, Co-doping with Magnesium and Silicon 67 References in Chapter 3 80 Chapter 4 Long-tail Effect and Optical Properties of Mn in GaN-based Up-converter Grown by Metal-Organic Vapor-Phase Epitaxy 82 4.1 Memory Effect, Redistribution of Mn and Up-converted Photoluminescence 82 4.2 Up-converter with Mn-doped Underlying GaN Intermediate Band Photodetection Layer and InGaN/GaN Multiple Quantum Wells Luminescence Layer 94 References in Chapter 4 107 Chapter 5 Intermediate Band Solar Cells with Mn-doped GaN Absorption Layer 112 5.1 PIN Structure with Mn-doped GaN Active Layer and P-AlGaN Blocking Layer 114 5.2 PIN Structure with Mn-doped GaN Active Layer and P-GaN Blocking Layer 133 5.3 Comparison of Device Characteristics between the PIN with P-AlGaN and P-GaN Blocking Layer 153 References in Chapter 5 157 Chapter 6 Intermediate Band Solar Cells with Mn-doped InxGa1-xN Absorption Layer 160 6.1 PIN Structure with Mn-doped In0.084Ga0.916N Active Layer 160 References in Chapter 6 176 Chapter 7 Conclusions and Future Works 177 7.1 Conclusions 177 7.2 Future Works 179 Publication List 181 Figure Captions Fig. 1-1. The band diagram and concept of an intermediate band solar cell. 4 Fig. 1-2. Limiting efficiency for the ideal IB solar cell, a two-terminal ideal tandem solar cell and an ideal single band gap solar cell. 4 Fig. 1-3. Upper limit of efficiency for the up-converting system as a function of the band gap. 7 Fig. 1-4. Efficiency of the down-converter system as a function of the band-gap. 7 Fig. 1-5. Technology tree for spin-based devices and their potential applications. 10 Fig. 1-6. Predicted Curie temperature as a function of bandgap and some experimentally reported values in the literature. 10 Fig. 2-1. The schematic of solar cell. 19 Fig. 2-2. The radiation spectrums of the black-body at 5762 K, AM0 and AM1.5 global. 23 Fig. 2-3. The solar spectrums at various air mass conditions. 23 Fig. 2-4. Process of photon absorption in the direct band gap semiconductor for an incident photon with energy hν = E2 - E1＞Eg. 24 Fig. 2-5. Process of photon absorption in the indirect band gap semiconductor for an incident photon with energy hν＜E2 - E1 and hν＞E2 - E1. The energy and momentum in each case are conserved by the absorption and emission of a phonon. 24 Fig. 2-6(a). The absorption coefficient as a function of photon energy for GaAs (direct band gap, 1.4 eV) and Si (indirect band gap, 1.12 eV). 25 Fig. 2-6(b). The absorption coefficient as a function of photon energy for GaN (direct band gap, 3.4 eV) at room temperature (300 K). 25 Fig. 2-7. Various recombination processes in the semiconductor. 31 Fig. 2-8. Surface states at the interface of semiconductors. 31 Fig. 2-9. A solar cell circuit model. The diode 1 represents the recombination current in the quasi-neutral regions and the diode 2 represents the recombination in the depletion region. 35 Fig. 2-10. Typical current-voltage characteristic of a solar cell (Si). 35 Fig. 2-11. Solar cell circuit model characteristics including the parasitic series and shunt resistances. 35 Fig. 2-12. Effect of series resistance on I-V curve of a solar cell as Rsh→∞. 36 Fig. 2-13. Effect of shunt resistance on I-V curve of a solar cell as Rs→0. 36 Fig. 2-14. Maximum theoretical efficiency for a simple model as a function of semiconductor band gap for an AM1.5 global solar spectrum. 38 Fig. 2-15. The band diagram of a semiconductor p-n junction solar cell. 41 Fig. 2-16. The SQ limit of efficiency for a solar cell as a function of band gap energy. Curve (a) unconcentrated 6000 K black body radiation (b) full concentrated 6000 K black body radiation (c) unconcentrated AM1.5-Direct and (d) AM1.5 Global. 41 Fig. 2-17. Band diagram of the intermediate band solar cell. 45 Fig. 2-18(a). The structure of the intermediate band solar cell (b) band diagram in equilibrium (c) band diagram of forward bias conditions. 45 Fig. 2-19. Efficiency limiting for the intermediate band solar cell under maximum concentrated sunlight, single-gap solar cell and a tandem of two cells that series-connected. 46 Fig. 2-20. The location of estimated Mn-level as a function of the In content in InGaN. 46 Fig. 2-21. Efficiency limiting of InGaN: Mn intermediate band solar cell in the calculation of maximum concentration for AM 1.5 Direct spectrums and for the sun assumed as a blackbody at 6000 K. 47 Fig. 2-22. The equivalent circuit of the IB solar cell. 47 Fig. 2-23. The design of structure for the up-convertion system. 49 Fig. 2-24. The diagram of energy levels in the up-convertion system. 49 Fig. 2-25. The equivalent circuit of the up-conversion system. 49 Fig. 2-26. The upper limits for the conversion efficiency of the up-conversion system as a function of the band gap. 49 Fig. 2-27. The design of structure for the down-convertion system. 50 Fig. 2-28. The equivalent circuit of the down-conversion system. 50 Fig. 2-29. The upper limits for the conversion efficiency of the down-conversion system as a function of the band gap. 50 Fig. 3-1. Schematic diagram of a bubbler and the gas flow of the MO source. The MO precursor carried can flow into the run or vent line. In our group, the carrier gas is N2. 54 Fig. 3-2. The detailed value of parameters and the vapor pressure equation (and curve) for the metal-organic precursor of manganese used in our group. 54 Fig. 3-3. The photo of the MOVPE system used in our laboratory. 58 Fig. 3-4. The secondary Mn ion counts as a function of the Mn precursor molar flow rate. 59 Fig. 3-5. The secondary Mn ion counts as a function of the growth temperature. 59 Fig. 3-6. The secondary Mn ion counts as a function of the growth pressure. 60 Fig. 3-7. The secondary Mn ion counts as a function of the H2 ambient flow rate. 60 Fig. 3-8(a). The secondary Mg ion counts as a function of the Mn source flow rate (b) the secondary Si ion counts as a function of the Mn source flow rate. 61 Fig. 3-9. The appearance of the undoped, lightly Mn-doped and heavily Mn-doped GaN samples from left to right, respectively. 63 Fig. 3-10. The surface morphology of Mn-doped GaN observed by the polarizing optical microscopy in different Mn source flow rate (0, 50 and 500 sccm) at 50X and 200X magnification. 64 Fig. 3-11. The atomic force microscopy (AFM) for the undoped (0sccm), lightly Mn-doped (50sccm) and heavily Mn-doped (500sccm) GaN. 64 Fig. 3-12(a). X-ray diffraction (XRD) (002) rocking curve spectra (b) X-ray diffraction (XRD) (102) rocking curve spectra for GaN epitaxial layers with different Mn doping level. 65 Fig. 3-13. The surface morphology of Mn-doped InGaN observed by the polarizing optical microscopy in different Mn source flow rate (0, 100 and 200 sccm) at 50X and 200X magnification. 66 Fig. 3-14. The (004) X-ray diffraction (XRD) ω-2θ spectra for InGaN bulk with different Mn doping level. 66 Fig. 3-15. The bulk Mn-doped GaN 300 K transmission spectra with the different Mn atom incorporation controlled by altering the carrier gas flow rate (sccm). 71 Fig. 3-16(a). The bulk Mn-doped GaN 20 K photoluminescence (PL) spectra with the different Mn atom incorporation controlled by altering the carrier gas flow rate (sccm) (b) y-scale magnification. 72 Fig. 3-17. The unintentional doped and Mn-doped InGaN 300 K transmission spectra. 73 Fig. 3-18(a). The Mn-doped InGaN 300 K photoluminescence (PL) spectra with the different Mn atom incorporation controlled by altering the carrier gas flow rate (sccm) and (b) shows the magnification of y-scale. 74 Fig. 3-19. The effect of Mn doping (controlled by altering the carrier gas flow rate) on the electrical properties of the unintentionally doped GaN (u-GaN), Si-doped GaN (n-GaN) and Mg-doped GaN (p-GaN). 75 Fig. 3-20. The SQUID 300 K magnetic hysteresis loop of the Mn-doped GaN on u-GaN (n~1017cm-3) template with different Mn incorporation level in the horizontal magnetic field. 75 Fig. 3-21. The SQUID 300 K magnetic hysteresis loop of the Mn-doped GaN on p-GaN template with different Mn doping level in the horizontal magnetic field. 76 Fig. 3-22. The SIMS profile for the Mn-doped GaN on p-GaN template. 76 Fig. 3-23. The SQUID 300 K magnetic hysteresis loop of Mn-doped GaN on u-GaN template (n~1017cm-3) with different Mg co-doping levels in the horizontal magnetic field. 77 Fig. 3-24(a). The Ga 3d x-ray photoelectron spectroscopy (XPS) measurements of the GaN and GaN: Mn samples. (b) The N 1s x-ray photoelectron spectroscopy (XPS) measurements of the GaN and GaN: Mn samples. 78 Fig. 3-25. The transmission spectra of the Mn-doped GaN co-doping with the different Mg atom incorporation. 79 Fig. 3-26. The 300 K relative external quantum efficiency (EQE) of the Mn-doped GaN co-doping with the different Mg atom incorporation. 79 Fig. 4-1(a)-(d). Schematic structures in cross-section view for the samples A, B, C and D regrown with varied chamber treatments, respectively. (e)-(f) Schematic structures in cross-section view for the samples E and F grown on Mn-doped GaN templates without and with HCl surface treatments, respectively. 90 Fig. 4-2. Low temperature (12 K) PL spectra of samples A and B excited by (a) 325 nm He-Cd laser and (b) 488 nm Ar laser (c) SIMS profiles of Ga, In, Mn and Si elements taken from the sample B as a function of depth from the surface. 91 Fig. 4-3. Low temperature (12 K) PL spectra of samples A, C and D excited by (a) 325 nm He-Cd laser (b) 488 nm Ar laser. 92 Fig. 4-4. SIMS profiles of Ga, In, Mn and Si elements taken from the (a) sample C and (b) sample D. 92 Fig. 4-5. SIMS profiles of Mn element taken from the samples E and F. 93 Fig. 4-6(a). XRD (004) spectra of the samples C and D for determination of indium composition in QWs (b) XRD (004) spectra for determination of indium composition of the bulk Mn-doped InGaN epitaxial layers grown with different Mn flow rates. 93 Fig. 4-7. Schematic device structure in cross-section view: (a) samples A, (b) samples B, (c) samples C and (d) samples D. 101 Fig. 4-8. Low temperature (12 K) PL spectra of samples A and B for the indicated (a) 325 nm He-Cd laser excitation and (b) 488 nm Ar laser excitation. 102 Fig. 4-9. Low temperature (12 K) PL spectra for the 488 nm (2.54 eV) Ar laser excitation of samples A, B, C and D. 103 Fig. 4-10. Typical room temperature (300 K) spectral responsivity of the PD-I (sample C) and PD-II (sample D) taken at zero bias. 104 Fig. 4-11. 488 nm (Eexc = 2.54 eV) Ar laser incident pump power dependence of the spectrally up-converted PL emission intensity of samples A at low temperature (12 K). The lines show the linear regression in the double-logarithmic plot. The slope of n = 0.9 is also indicated. 105 Fig. 4-12. Schematic band diagram of sample A and the up-converted PL excitation process resulting in emission at 2.99 eV (Eemi = 2.99 eV) and 3.51 eV (Eemi = 3.51 eV). 106 Fig. 5-1. Concept of the intermediate band solar cell operation including an intermediate band with partially filled with electrons within the host semiconductor band gap. 113 Fig. 5-2. Schematic devices structures of the sample A, B, C and D. 121 Fig. 5-3. Schematic dual-light source setup for determining the relative external quantum efficiency of the GaN IB solar cells with Mn-doped absorption layer. 121 Fig. 5-4(a). Typical room temperature current-density-versus-voltage (J-V) characteristics of the solar cells under forward bias in the darkness (b) reverse bias for sample A, B, C and D. 122 Fig. 5-5(a)(b). Typical I-V characteristics of the n- and p-electrode contacts, respectively. The I-V curves were measured from two adjacent contacts (100 μm × 200 μm) with a spacing of 5 μm. (c) Typical value of specific contact resistance and sheet resistance for n- and p-electrode of sample A, B, C and D. 124 Fig. 5-6(a). Typical Hall data for different Mn doping level for GaN: Mn, n-GaN: Mn and p-GaN: Mn. (b) Typical SIMS profile data for sample A, B, C and D. (c) Typical Al element for SIMS profile data of sample A, B, C and D. (d) Typical XRD (002) ω-2θ for sample A, B, C and D. 126 Fig. 5-7. Typical current density-voltage characteristics of sample A, B, C and D under AM1.5G illumination. 127 Fig. 5-8(a). Typical Voc as a function of Mn flow rate. (b) Typical Jsc as a function of Mn flow rate. (c) Typical FF as a function of Mn flow rate. (d) Typical efficiency as a function of Mn flow rate. 129 Fig. 5-9. Typical bulk Mn-doped GaN 20 K photoluminescence (PL) spectra with the different Mn atom incorporation controlled by altering the carrier gas flow rate (sccm). 130 Fig. 5-10. Typical room-temperature transmission spectra measured from the sample A, B, C and D. 130 Fig. 5-11. Typical relative external quantum efficiency taken from sample A, B, C and D with lock-in amplifier techniques at room temperature. 131 Fig. 5-12(a). Typical relative external quantum efficiency taken from sample A and B with power-dependent dual-light source excitation and lock-in amplifier techniques. (b) Relative EQE of sample B as a function of 405 nm laser power corresponding to three locked photon energies. 132 Fig. 5-13. Schematic devices structures of the sample A, B, C, D, E and F. 140 Fig. 5-14(a). Typical room temperature current-density-versus-voltage (J-V) characteristics of the solar cells under forward bias in the darkness. (b) Reverse bias for sample A, B, C, D, E and F. 141 Fig. 5-15(a)(b). Typical I-V characteristics of the n- and p-electrode contacts, respectively. The I-V curves were measured from two adjacent contacts (100 μm × 200 μm) with a spacing of 5 μm. (c) Typical value of specific contact resistance and sheet resistance for n- and p-electrode of sample A, B, C, D, E and F. 143 Fig. 5-16(a)(b). Typical 300 K photoluminescence (PL) spectra of the sample A, B, C, D, E and F. 144 Fig. 5-17. Typical SIMS profile data for sample A, B and E. 145 Fig. 5-18. Typical current density-voltage characteristics of sample A, B, C, D, E and F under AM1.5G illumination. 145 Fig. 5-19(a). Typical Voc as a function of Mn flow rate. (b) Typical Jsc as a function of Mn flow rate. (c) Typical FF as a function of Mn flow rate. (d) Typical efficiency as a function of Mn flow rate. 147 Fig. 5-20. Typical relative external quantum efficiency taken from sample A, B and E with lock-in amplifier techniques at room temperature. 148 Fig. 5-21(a). Typical relative external quantum efficiency taken from sample A and B with power-dependent dual-light source excitation and lock-in amplifier techniques. (b) Relative EQE of sample B as a function of 405 nm laser power corresponding to three locked photon energies. 149 Fig. 5-22(a). Typical relative external quantum efficiency taken from sample A and E with power-dependent dual-light source excitation and lock-in amplifier techniques. (b) Relative EQE of sample E as a function of 405 nm laser power corresponding to three locked photon energies. 150 Fig. 5-23(a). 300 K electroluminescence (EL) emission photos from the sample A, B, C, D, E and F taken at 150 mA current injection. (b) (c) 300 K electroluminescence spectra (EL) from the sample A, B, C, D, E and F taken at 150 mA current injection. 152 Fig. 5-24. The typical (a) Voc (b) Jsc (c) FF (d) efficiency as a function of Mn doping level for PIN structure with p-AlGaN and p-GaN blocking layer. 156 Fig. 6-1. Schematic structures of sample A and B. 167 Fig. 6-2(a). Typical room temperature current-density versus voltage (J-V) characteristics of the sample A and B under forward bias. (b) Reverse bias in the darkness. 168 Fig. 6-3(a)(b). Typical I-V characteristics of the n- and p-electrode contacts onto n- and p-GaN taken from the sample A and B, respectively. The I-V curves were measured from two adjacent contacts (100 μm × 200 μm) with a spacing of 5 μm (c) a list of the typical specific contact resistances and sheet resistances taken from the sample A and B. 170 Fig. 6-4. The typical SIMS depth profile of the sample B. 170 Fig. 6-5(a)(b). Typical (002) and (004) X-ray diffraction (XRD) ω-2θ spectra for sample A and B. 171 Fig. 6-6. Typical 300 K PL spectra taken from sample A and B. 172 Fig. 6-7. Typical current-density versus voltage characteristics of sample A and B under AM1.5G illumination. 172 Fig. 6-8. Typical Voc, Jsc, FF and efficiency of sample A and B. 173 Fig. 6-9. Typical transmission spectra taken from sample A and B at 300 K. 173 Fig. 6-10(a). Typical relative external quantum efficiency (EQE) taken from sample A and B with dual-light-source excitation and lock-in amplifier techniques without 405 nm (3.06 eV) laser illumination at 300 K (b) the dual-light-source excitation taken from the sample B. A power-dependent 405 nm (3.06 eV) laser source (not chopped) was applied to sample B during the measurement of relative external quantum efficiency (EQE). 174 Fig. 6-11(a). 300 K electroluminescence (EL) emission photos from the sample A and B taken at 150 mA current injection (b) 300 K electroluminescence spectra (EL) taken from the sample A and B at 150 mA current injection. 175

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    References in Chapter 2

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    References in Chapter 6

    [1] A. Luque and A. Marti, “Increasing the efficiency of ideal solar cells by photon induced transitions at intermediate levels,” Phys. Rev. Lett., vol. 78, pp. 5014-5017, 1997.
    [2] A. Luque and A. Marti, “A metallic intermediate band high efficiency solar cell,” Prog. Photovolt: Res. Appl., vol. 9, pp. 73-86, 2001.
    [3] A. Marti, C. Tablero, E. Antolin, A. Luque, R. P. Campion, S. V. Novikov and C. T. Foxon, “Potential of Mn doped In1-xGaxN for implementing intermediate band solar cells,” Sol. Energy Mater. Sol Cells, vol. 93, pp. 641-644, 2009.

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