Yongkook Park

Casting Single Crystal Silicon: Novel Defect Profiles from BP Solar's Mono2 TM Wafers

A novel crystal growth method has been developed for the production of ingots, bricks and wafers for solar cells. Monocrystallinity is achievable over large volumes with minimal dislocation incorporation. The resulting defect types, densities and interactions are described both microscopically for wafers and macroscopically for the ingot, looking closely at the impact of the defects on minority carrier lifetime. Solar cells of 156 cm2 size have been produced ranging up to 17% in efficiency using industrial screen print processes.

Extremely Low Contact Resistance on Graphene through n-Type Doping and Edge Contact Design

The effects of graphene n-doping on a metal-graphene contact are studied in combination with 1D edge contacts, presenting a record contact resistance of 23 Ω μm at room temperature (19 Ω μm at 100 K). This contact scheme is applied to a graphene-perovskite hybrid photodetector, significantly improving its performance (0.6 → 1.8 A W(-1) in photoresponsivity and 3.3 × 10(4) → 5.4 × 10(4) Jones in detectivity).

Broad Detection Range Rhenium Diselenide Photodetector Enhanced by (3‐Aminopropyl)Triethoxysilane and Triphenylphosphine Treatment

The effects of triphenylphosphine and (3-aminopropyl)triethoxysilane on a rhenium diselenide (ReSe2 ) photodetector are systematically studied by comparing with conventional MoS2 devices. This study demonstrates a very high performance ReSe2 photodetector with high photoresponsivity (1.18 × 10(6) A W(-1) ), fast photoswitching speed (rising/decaying time: 58/263 ms), and broad photodetection range (possible above 1064 nm).

Deep level transient spectroscopy and capacitance-voltage study of dislocations and associated defects in SiGe∕Si heterostructures

Three SiGe∕Si heterostructures with different Ge contents have been examined by deep level transient spectroscopy (DLTS) and capacitance-voltage techniques. DLTS revealed a broad band of traps from 80to250K in the as-grown samples. Arrhenius plots of a 25% SiGe sample revealed three trap levels at 0.28, 0.31, and 0.43eV above the valance band, respectively. By varying the reverse biases and comparing samples of different Ge contents, it was found that the trap levels shift toward the valance band with increasing Ge concentration. Capacitance-voltage data indicated that the acceptor trap levels in the SiGe graded layer dramatically decreased from 40×1013cm−3 in the as-grown sample to 4×1013cm−3 after annealing at over 800°C. Based on their charge states and thermal annealing behaviors, we suggest that majority of the grown-in acceptor levels are likely due to vacancy clusters generated by dislocation jog dragging, which can be readily annealed out, leaving only the dislocation related deep levels. The dens...

Hydrogen passivation of deep energy levels at the interfacial grain boundary in (110)/(100) bonded silicon wafers

This letter evaluates the density of grain boundary (GB) states before and after hydrogenation by J-V, C-V, and capacitance transient methods using gold/direct silicon-bonded (DSB) (110) thin silicon top layer/(100) silicon substrate junctions. The GB potential energy barrier in thermal equilibrium was reduced by 70 meV from 0.46 eV (before hydrogenation) to 0.39 eV (after hydrogen treatment). Whereas the clean sample had a density of GB states of ∼6×1012 cm−2 eV−1 in the range of Ev+0.54–0.64 eV, hydrogenation reduced the density of GB states to ∼9×1011 cm−2 eV−1 in the range of Ev+0.56–0.61 eV, which is about a sevenfold reduction from that of the clean sample.

Impact of structural defect density on gettering of transition metal impurities during phosphorus emitter diffusion in multi-crystalline silicon solar cell processing

AbstractThe impact of structural defect density on gettering of transition metal impurities during phosphorous emitter diffusion has been investigated using a pair of multi-crystalline silicon (mc-Si) wafers. Chromium (Cr) impurities incorporated during growth were identified by deep level transient spectroscopy (DLTS) and used to evaluate the gettering efficiency. The Cr impurity concentration in the low defect density region of mc-Si wafers was reduced from ~3.5 × 1013 cm−3 to ~1.7 × 1012 cm−3 after phosphorous diffusion gettering (PDG), while for the high defect density region, there is no appreciable variation in the Cr concentration which only changed from ~3.0 to ~2.2 × 1012 cm−3 following PDG. It was concluded that the gettering process is not effective for highly defective regions of mc-Si wafers due to the ineffective impurity release from structural defects during the PDG process.

Theoretical and Experimental Investigation of Graphene/High-

Here, we theoretically and experimentally investigate the impact of a high-κ layer inserted between graphene and p-Si in a graphene/Si junction. We have achieved 86-fold and 222-fold reductions in a specific contact resistivity (ρ_c) by inserting 1-nm-thick Al₂O₃ and 2-nm-thick TiO₂ in the graphene-semiconductor junction, respectively, corresponding to lowering the effective barrier height by 0.24 and 0.12 eV. Furthermore, we propose a graphene-induced gap state model that simultaneously considers the graphenes modulation by a gate bias and the effect of the high-κ insertion.

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The effects of graphene n-doping on metal-graphene (M-G) contacts in combination with 1D edge contacts is discussed by J.-H. Park and co-workers, as described on page 864, presenting a record contact resistance of 23 Ω μm at room temperature (19 Ω μm at 100 K). This is lower than the value required for the latest Si CMOS technology. This contact scheme is applied to graphene-perovskite hybrid photo-detectors, significantly improvement of its performance (0.6 → 1.8 A W(-1) in photoresponsivity and 3.3 × 10(4) → 5.4 × 10(4) Jones in detectivity).

/p-Si Junctions

This article examined the electrical activities of dislocations in a SiGe/Si heterostructure by deep level transient spectroscopy (DLTS) after iron contamination and phosphorous diffusion gettering. DLTS of iron contaminated samples revealed a peak at 210 K, which was assigned to individual iron atoms or very small (<2 nm) precipitates decorated along dislocations, considering that the iron contamination annealing was terminated by quenching and transmission electron microscopy did not reveal any precipitate at dislocations. Arrhenius plot of the 210 K peak yielded a hole capture cross section of 2.4×10−14 cm2 and an energy level of 0.42 eV above the valance band. The relatively large hole capture cross section indicates strong interactions between iron-related deep levels and the dislocation shallow bands. DLTS of the iron contaminated sample revealed that 6×1014 cm−3 of boron can more effectively trap interstitial iron at room temperatures than the strain field/defect sites at 107–108 cm−2 dislocations....

Graphene: Extremely Low Contact Resistance on Graphene through n-Type Doping and Edge Contact Design (Adv. Mater. 5/2016)

In this article, the impact of hydrogenation on the electrical properties of impurity (Fe)-contaminated silicon grain boundaries (GBs) is investigated using capacitance-voltage (C-V) and capacitance transient (C-t) techniques with hybrid orientation direct-silicon-bonded (DSB) wafers. The samples consist of a 2.3 μm thick (110) Si layer on a p-type (100) Si substrate produced via hydrophilic wafer bonding, cleavage, and epithickening. It was found that for a relatively clean GB, the density of the GB states (DGB) is ∼6 × 1012 eV−1cm−2, and the charge neutral level is ∼0.53 eV from the valance band. DGB increases to more than 2 × 1013 eV−1cm−2after the Fe contamination, which is reduced to ∼1 × 1013 eV−1cm−2 after the hydrogenation treatment. The charge neutral level, which shifts toward the conduction band after the Fe contamination, is reversed after hydrogenation.