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Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells
摘要： As-doped polycrystalline ZnTe layers grown by metalorganic chemical vapor deposition (MOCVD) have been investigated as a back contact for CdTe solar cells. While undoped ZnTe ?lms were essentially insulating, the doped layers showed signi?cant rise in conductivity with increasing As concentration. High p-type carrier densities up 4.5 × 1018 cm?3 was measured by the Hall-e?ect in heavily doped ZnTe:As ?lms, displaying electrical properties comparable to epitaxial ZnTe single crystalline thin ?lms in the literature. Device incorporation with as-deposited ZnTe:As yielded lower photovoltaic (PV) performance compared to reference devices, due to losses in the open-circuit potential (VOC) and ?ll factor (FF) related to reducing p-type doping density (NA) in the absorber layer. Some minor recovery observed in absorber doping following a Cl-free post–ZnTe:As deposition anneal in hydrogen at 420 ?C contributed to a slight improvement in VOC and NA, highlighting the signi?cance of back contact activation. A mild CdCl2 activation process on the ZnTe:As back contact layer via a sacri?cial CdS cap layer has been assessed to suppress Zn losses, which occur in the case of standard CdCl2 anneal treatments (CHT) via formation of volatile ZnCl2. The CdS sacri?cial cap was e?ective in minimising the Zn loss. Compared to untreated and non-capped, mild CHT processed ZnTe:As back contacted devices, mild CHT with a CdS barrier showed the highest recovery in absorber doping and an ~10 mV gain in VOC, with the best cell e?ciency approaching the baseline devices.
关键词： solar cells,CdTe,metalorganic chemical vapor deposition (MOCVD),ZnTe:As back contact,thin ?lms
更新于2025-09-11 14:15:04
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Influence of the growth conditions of LT-AlN on quality of HT-AlN growth on Si (111) by metalorganic chemical vapor deposition
摘要： In this study, AlN films on Si(111) using LT-AlN nucleation layer with various conditions at TMAl preflow were grown and investigated. It was shown that the main factor influencing the quality of AlN films is the degree of the substrate coating by aluminium at preflow. The qualitative model of AlN growth using the LT-AlN nucleation layer for three different coverage by Al (high, optimal and low) was suggested. For the film grown under optimal conditions, the rocking curve FWHM for the AlN (0002) reflection was 0.59о. The demonstrated possibility of the high-quality growth of AlN films below 1000oС would be useful for high power electronics.
关键词： B1. Silicon,B1. Aluminum Nitride,B1. Nitrides,B2. Semiconducting III–V materials,A3. Metalorganic chemical vapor deposition,A1. Crystal structure
更新于2025-09-10 09:29:36
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Thermal Annealing Effects on the Electrical and Structural Properties of Ni/Pt Schottky Contacts on the Quaternary AlInGaN Epilayer
摘要： Pt/Au, Ni/Au, Ni/Pt/Au Schottky contacts were placed on a quaternary Al0.84In0.13Ga0.03N epilayer. The electrical and structural properties of the as-deposited Pt/Au, Ni/Au, Ni/Pt/Au and annealed Ni/Pt/Au Schottky contacts were investigated as a function of annealing temperature using current–voltage (I–V), capacitance–voltage (C–V), and high resolution x-ray diffraction measurements (HR-XRD). According to the I–V, Norde, and C–V methods, the highest Schottky barrier height (SBH) was obtained for the Pt/Au (0.82 eV (I–V), 0.83 eV (Norde), and 1.09 eV (C–V)) contacts when they were compared with the other as-deposited Schottky contacts. The estimated SBH of the annealed Ni/Pt/Au Schottky contacts, calculated from the I–V results, were 0.80 eV, 0.79 eV, and 0.78 eV at 300°C, 400°C, and 500°C, respectively. The SBH decreases with an increase in the annealing temperature up to 500°C compared with that of the as-deposited Ni/Pt/Au Schottky contact. The observed extra peaks in the annealed samples confirm the formation of a new interfacial phase at the interface. However, the diffraction patterns of the annealed Schottky contacts did not change as a function of the annealing temperature. The higher ideality factors values were obtained for as-deposited Pt/Au (5.69), Ni/Au (6.09), and Ni/Pt/Au (6.42) Schottky contacts and annealed Ni/Pt/Au (6.42) Schottky contacts at 300°C (6.89), 400°C (7.43), and 500°C (8.04). The higher n results can be attributed to current-transport mechanisms other than thermionic emission, such as dislocation related tunneling.
关键词： A3. metalorganic chemical vapor deposition (MOCVD),annealing effects,A1. Schottky,B1. AlInGaN
更新于2025-09-10 09:29:36
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Investigation of GaN-on-GaN vertical <i>p</i> - <i>n</i> diode with regrown <i>p</i> -GaN by metalorganic chemical vapor deposition
摘要： To mimic selective-area doping, p-GaN was regrown on an etched GaN surface on GaN substrates by metalorganic chemical vapor deposition. Vertical GaN-on-GaN p-n diodes were fabricated to investigate the effects of the etch-then-regrowth process on device performance. The crystal quality of the sample after each epitaxial step was characterized by X-ray diffraction, where the etch-then-regrowth process led to a very slight increase in edge dislocations. A regrowth interfacial layer was clearly shown by transmission electron microscopy. Strong electroluminescence was observed with three emission peaks at 2.2 eV, 2.8 eV, and 3.0 eV. The forward current density increased slightly with increasing temperature, while the reverse current density was almost temperature independent indicating tunneling as the reverse transport mechanism. This result is very similar to the reported Zener tunnel diode comprising a high doping pro?le at the junction interface. High levels of silicon and oxygen concentrations were observed at the regrowth interface with a distribution width of (cid:2)100 nm. This work provides valuable information on p-GaN regrowth and regrown GaN p-n diodes, which can serve as an important reference for developing selective doping for advanced GaN power electronics for high voltage and high power applications.
关键词： electroluminescence,tunneling,GaN,regrowth,p-n diode,metalorganic chemical vapor deposition
更新于2025-09-10 09:29:36
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Compensation effects of high oxygen levels in semipolar AlGaN electron blocking layers and their mitigation via growth optimization
摘要： InGaN-based laser diodes (LDs) grown on the semipolar plane of GaN offer advantages arising from predicted higher gain compared to c-plane devices. However, the performance of semipolar devices has been limited by low injection efficiency. In prior work, this has been proposed to be caused by an inefficient AlGaN electron blocking layer (EBL). A high oxygen level in the EBL found in previous work could cause compensation of the p-type dopants. In this work the oxygen impurities were eliminated via optimizations during the metalorganic chemical vapor deposition (MOCVD) growth. Optimization of the V/III ratio and an increase in the growth temperature during the AlGaN growth was found to reduce the oxygen incorporation. Additionally, residual sources of oxygen were removed from the MOCVD growth process. These combined steps reduced the peak oxygen level in the AlGaN from 5 × 1018/cm3 to 6 × 1017/cm3 as measured by secondary ion mass spectroscopy. LDs were fabricated with and without these modifications to clarify the effect of the reduced oxygen. The threshold current and differential efficiency showed improvement with reduced oxygen. The internal loss and gain of these LDs were measured using the segmented contact method, confirming that the injection efficiency was boosted from 60% with high oxygen to 80% with low oxygen.
关键词： B2. Semiconducting aluminum compounds,A3. Metalorganic chemical vapor deposition,B3. Laser diodes,B1. Nitrides,A1. Impurities
更新于2025-09-09 09:28:46
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Structural characteristics of m-plane AlN substrates and homoepitaxial films
摘要： Homoepitaxial non-polar AlN films were realized on m-plane (1010)-oriented AlN single crystals by metalorganic chemical vapor deposition (MOCVD). The microstructural properties of m-plane AlN substrates and homoepitaxial films were assessed by means of atomic force microscopy and high resolution x-ray diffraction characterization. Results indicated that both m-plane AlN substrates and films possessed exceptional structural quality, with some anisotropic mosaic distributions due to the quasi-bulk nature of the non-polar single crystals. An increase in the MOCVD growth temperature was noted to minimize the degree of inherited mosaic anisotropy without altering the m-plane AlN film growth rate, indicating that high temperature growth is critical to produce optimal film crystallinity. A dramatic change in the film surface morphology from heavily faceted “slate-like” features to monolayer steps was observed as the growth temperature was increased. The “slate-like” surface morphology produced low intensity cross-streaks in symmetric (1010) reciprocal space maps, tilted about 18° away from the (1010) crystal truncation rod. The orientation of these diffuse streaks corresponds to the physical alignment of the slates with respect to the substrate surface normal. X-ray line scans and defect-selective reciprocal space mapping confirmed that these low intensity streaks are solely dependent on this peculiar surface structure produced at low MOCVD growth temperatures and unrelated to basal plane stacking faults or other extended defects. All observations confirm that high quality III-nitride epitaxial structures on m-plane AlN substrates are attainable with controllable MOCVD growth processes, as demanded for future high performing AlN-based non-polar devices.
关键词： Characterization,Metalorganic chemical vapor deposition,High resolution x-ray diffraction,Surface structure,Nitrides,Crystal structure
更新于2025-09-04 15:30:14