Pn Junction Interface Research Articles

Characterizing electric fields in semiconductor devices: effect of second-harmonic light interference.

Characterizing electric fields in semiconductor devices using electric field-induced second-harmonic generation (EFISHG) has opened new opportunities for an advanced device design. However, this new technique still has challenges due to the interference between background second-harmonic generation (SHG) and EFISHG generated light. We demonstrate that interference effects can effectively be eliminated during EFISHG measurements by focusing the laser from the transparent substrate side of a GaN PN diode, enabling straightforward quantitative electric field analysis, in contrast to PN junction interface side measurements. A model based on wave generation and propagation is proposed and highlights the incoherence between background SHG and EFISHG light. This incoherence may be attributed to the depth of focus of the incident laser and phase mismatch between incident and SHG light.

A transparent photovoltaic device of Cu2O/SnO2 QDs/SnO2 pn junction with difunctional homogeneous SnO2 QDs transition layer

Carrier efficiency is the most crucial factor for the transparent photovoltaic devices. In this work, the Cu2O/SnO2 QDs/SnO2 pn junction transparent photovoltaic device is fabricated via a continuous sputtering-chemical-annealing method. As revealed, the as-prepared transparent photovoltaic device exhibits high transparency of ∼80% in visible light, noticeable photovoltaic conversion enhancement of ∼1.1 × 103 folds, and decent stability during the 20,000 s cycle. It could be mainly ascribed to that the SnO2 QDs with high quantum yield and appropriate potential can accelerate charge carrier injection and separation/migration for increasing carrier efficiency. Additionally, the SnO2 QDs with multiple reflections/interference can improve pn junction interface and increase solar efficiency while being transparent.

Influence of emitter position of silicon heterojunction photovoltaic solar cell modules on their potential-induced degradation behaviors

Potential-induced degradation (PID)-test results of modules fabricated from the rear- and front-emitter silicon heterojunction (SHJ) solar cells were compared to clarify the influence of the emitter position of SHJ photovoltaic (PV) cell modules on their PID behaviors. The PID tests were performed by applying a bias of −2000 V to the shorted interconnector ribbons from the front surface of the cover glass, at 85 °C. In the initial stage, both modules showed the same degradation characterized by a reduction in the short-circuit current density (Jsc). After the first-stage degradation, the rear-emitter SHJ PV modules exhibited subsequent degradation characterized by a significant reduction in the Jsc and open-circuit voltage (Voc), due to the enhancement of the minority-carrier recombination in the front surface region of the n-type crystalline silicon base. The front-emitter SHJ PV modules, on the other hand, showed a reduction in the fill factor (FF), in addition to moderate reductions in Jsc and Voc. The FF reduction of the front-emitter SHJ PV modules is considered to be caused by the enhancement of the recombination in the front surface region of the n-type crystalline-silicon base as the region corresponds to the pn junction interface of the front-emitter configuration. The moderate reductions in both Jsc and Voc may be due to further progression of the first-stage degradation. These findings are essential for understanding the mechanism of PID in SHJ PV cell modules.

Highly efficient inverted organic light-emitting diodes with organic p-n junction as electron injection layer

Organic p-n junction (PNJ) composing of PEDOT:PSS(MoO3)/Bphen:Cs2CO3 is introduced as electron injection layer (EIL) in the bottom-emission inverted organic light-emitting diodes (BIOLEDs). The devices with PNJ of PEDOT:PSS/Bphen:Cs2CO3 or MoO3/Bphen:Cs2CO3 as EIL achieve maximum current efficiency of 87.3 cd/A and 86.6 cd/A and power efficiency of 69.4 lm/W and 63 lm/W, respectively, which are higher than that79.8 cd/A and 60 lm/W of the device with the n-doping Bphen:Cs2CO3 as EIL, and 51% and 55% improvement in the half operational lifetime. The injection of electrons from the interface of PNJ but not directly from the ITO cathode is more effectively comparison with conventional BIOLED with n-doped Bphen:Cs2CO3 as EIL. Thus, reducing the charge accumulation between the electrode and the organic electron transport layer (ETL), moreover, the PNJ is able to control the injection equilibrium of the carriers, and improve the efficiency and stability of the device.

Fabrication and electrical properties of axial and radial GaAs nanowire pn junction diode arrays

We report on the fabrications and characterizations of axial and radial GaAs nanowire pn junction diode arrays. The nanowires are grown on n-doped GaAs (111)B substrates using the Au-catalyzed vapor—liquid—solid mechanism by metal—organic chemical vapor deposition (MOCVD). Diethyl—zinc and silane are used as p- and n-type dopant precursors, respectively. Both the axial and radial diodes exhibit diode-like J—V characteristics and have similar performances under forward bias. Under backward bias, the axial diode has a large leakage current, which is attributed to the bending of the pn junction interface induced by two doping mechanisms in Au-catalyzed nanowires. The low leakage current and high rectification ratio make the radial diode more promising in electrical and optoelectronic devices.

Microstructure Control of Absorber Sb2S3 and p-Type Semiconductor CuSCN for Semiconductor-Sensitized Solar Cells (TiO2/Sb2S3/CuSCN)

Semiconductor-sensitized solar cells (SSSCs) were fabricated with a planar n-type TiO2 film, an antimony sulfide (Sb2S3) thin film as the absorber, and a transparent p-type CuSCN film. The deposition amount of Sb2S3 and the pn junction interface condition significantly affected the generation and recombination of photo carriers. Analysis of the microstructure and chemical state of the Sb2S3, and the microstructure of CuSCN films showed that the homogeneity of the Sb2S3 and CuSCN films, the oxidation of Sb2S3 and the CUSCN thickness determined the optimal amount of Sb2S3 and the highest photoelectric conversion efficiency. For the ETA solar cell with the highest photoelectric conversion efficiency (1.67%), Sb2S3 was deposited by sputtering (SP) and CuSCN by wiping (WI).

Highly sensitive and selective triethylamine-sensing properties of nanosheets directly grown on ceramic tube by forming NiO/ZnO PN heterojunction

Chemiresistive gas sensors with high sensitivity, selectivity and reliable fabrication potency for specific gas have been now expected for many applications. A highly sensitive and selective nanostructured triethylamine (TEA) gas sensor has been fabricated successfully by designing PN heterojunction consisting of ZnO nanosheets and NiO nanoparticles. The ZnO nanosheets directly grew on Al2O3 ceramic tubes by introducing a seed layer with a simple and cost-effective hydrothermal method. By employing pulsed laser deposition (PLD) method, the construction of NiO/ZnO PN heterojunction is highly controllable and reproducible. In comparison with ZnO nanosheet, the NiO/ZnO nanoparticle/nanosheet heterojunction exhibits much better sensing property to TEA gas. The depletion layer formed at the PN junction interface in NiO/ZnO sensor can greatly increase the resistance in air and decrease the resistance in TEA gas. Due to the general working principle and controllable growth strategy, this study provides a way for design and fabrication of the chemiresistive gas sensors with high performance.

The Effect of Intrinsic Defects on Resistive Switching Based on p–n Heterojunction

We report a unidirectional bipolar resistive switching in an n-type GaOx/p-type NiOx heterojunction fabricated by magnetron sputtering at room temperature. The resistive switching (RS) of the heterojunction directly relate with the concentration of intrinsic defects in oxide, such as oxygen vacancies and oxygen ions. Under external electric field, these electromigrated defects accumulate at the pn junction interface and modify the interface barrier, forming or rupturing the filamentary paths between n-GaOx and p-NiOx, leading to the switching between Ohmic and diode characteristics of the device.

Accurate determination of interface trap state parameters by admittance spectroscopy in the presence of a Schottky barrier contact: Application to ZnO-based solar cells

This work shows that when a Schottky barrier is present in a photovoltaic device, such as in a device with an ITO/ZnO contact, equivalent circuit analysis must be performed with admittance spectroscopy to accurately determine the pn junction interface recombination parameters (i.e., capture cross section and density of trap states). Without equivalent circuit analysis, a Schottky barrier can produce an error of ∼4-orders of magnitude in the capture cross section and ∼50% error in the measured density of trap states. Using a solution processed ZnO/Cu2O photovoltaic test system, we apply our analysis to clearly separate the contributions of interface states at the pn junction from the Schottky barrier at the ITO/ZnO contact so that the interface state recombination parameters can be accurately characterized. This work is widely applicable to the multitude of photovoltaic devices, which use ZnO adjacent to ITO.

Efficient tandem organic light-emitting device based on photovoltaic-type connector with positive cycle

We designed a tandem organic light-emitting device based on an organic photovoltaic-type charge generation connector (CGC) of fullerene carbon 60/copper(II) phthalocyanine. The CGC can absorb a portion of photons radiated from emission zone and form excitons which disassociated into free charges at PN junction interface without energy barrier, leading to low driving voltage and better charge balance. The efficiency increases remarkably with increasing current density, even beyond two folds compared with single unit device under higher current density, meaning slower roll-off. The whole process is a positive cycle, and actually enhances the utilization of internal radiation and the overall performance of tandem device.

Resistive switching in a GaOx-NiOx p-n heterojunction

We report a unidirectional bipolar resistive switching in an n-type GaOx/p-type NiOx heterojunction fabricated by magnetron sputtering at room temperature. The resistive switching behavior coincides with the switching between Ohmic conduction (low resistance) and rectifying behavior (high resistance) of the heterojunction diode. Under external electric field, electromigrated intrinsic defects, such as oxygen vacancies and oxygen ions, accumulate at the pn junction interface and modify the interface barrier, forming or rupturing the filamentary paths between n-GaOx and p-NiOx, leading to the switching between Ohmic and diode characteristics of the device. The device shows good endurance, retention performance, and scaling capability, signaling the potential of a diode-structured resistive switching device for non-volatile memory applications.

New Electrodeposition Technique for Controlling Depth Profile of CuInSe2 Thin Films for Solar Cell Application

It is known that the efficiency of CuInSe2 (CIS)-based solar cells can be improved using a CIS layer with a composition that can be modulated to be In-rich near the pn junction interface. In this work, a new electrodeposition technique for preparing CIS thin films with a controlled composition depth profile was developed. CIS thin films having a bilayer structure, that is, with the Cu-rich and In-rich layers, were successfully deposited from one electrolyte only by changing the substrate potential during electrodeposition.

Electroluminescence and photoluminescence characteristics in ZnTe LED fabricated by Al thermal diffusion

The origins of electroluminescence (EL) from ZnTe LED fabricated by Al thermal diffusion were investigated by comparing the depth dependence of photoluminescence (PL) spectra of Al thermal diffusion layer. The broad PL peak at 2.17 eV was observed predominantly near the surface of Al diffusion layer, which was assigned as a donor-acceptor pair (DAP) recombination emission due to AlZn donor and VZn-AlZn complex acceptor. At the interface of pn-junction, an emission due to P acceptor-related free to bound transition at 2.33 eV, and another DAP recombination emission at about 2.3 eV became strong while a DAP emission at 2.17 eV was weakened. At deeper part corresponding to p-type region, only a P acceptor bound excitonic emission at 2.37 eV and a free-to-bound emission peaks were observed. Based on these results, the origins of EL peaks were discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Mg-related Deep Levels in AlInP

The properties of deep levels found in Mg-doped AlInP, grown by metal-organic chemical vapor deposition, have been studied. Two distinct levels, labeled E1 and E2, were observed, with the activation energy of 0.19 and 0.514 eV, respectively. From distribution profiles measured on trap E1, E2 and Mg-dopant, all three concentration profiles have similar behaviors. The concentration increases gradually from the interface of pn junction. Furthermore, both trap E1 and E2 concentration increase with elevating Mg-dopant concentration. Thus, it seems that these deep levels originate from Mg-related defects.