N2O Plasma Research Articles

Growth of high quality polycrystalline InGaO thin films by spray pyrolysis for coplanar thin-film transistors on polyimide substrate

The current mobile devices are moving towards flexible electronics. Introducing crystalline oxide semiconductors on flexible substrates is important to satisfy the requirements of high-resolution displays on flexible substrates. This study investigates the low-cost, as-grown polycrystalline (Poly) InGaO thin film transistor by spray pyrolysis on polyimide (PI) substrate. Grazing Incidence X-ray Diffraction (GI-XRD) measurements demonstrate that In0.8Ga0.2O, In0.7Ga0.3O, and In0.5Ga0.5O compositions exhibit crystallization on-set temperatures of ∼330, ∼350, and ∼415°C, respectively. Poly-In0.7Ga0.3O thin film with lower oxygen-vacancy (∼15 %) and less than 5 % O-H group could be achieved at the substrate temperature of 370°C. The hysteresis-free device performance with an average saturation mobility of 43.73 cm2V−1s−1 has been obtained using the poly-In0.7Ga0.3O with optimized N2O plasma treatment on the poly-oxide thin film. The TFTs show remarkable stability under humid environments and various stress conditions such as positive bias temperature, negative bias temperature, and mechanical stresses. In addition, the 96-stage gate shift register made of poly-In0.7Ga0.3O TFTs by spray pyrolysis exhibits the rising and falling times of less than 820 ns. Therefore, the poly-In0.7Ga0.3O TFTs by spray pyrolysis could be used for high-resolution, cost-effective, flexible active-matrix light-emitting displays.

P‐97: Improved Electrical Performance and Realiability of a‐IGZO TFT by N2O Plasma Treatment Optimization

This study investigates the abnormal reliability degradations observed under positive bias temperature stress (PBTS) in a‐IGZO TFTs treated by N2O plasma treatment and proposes a solution according to the presence of N2O plasma in the subsequent postprocess. In mass manufacture of a‐IGZO TFTs, N2O plasma is usually completely removed during the subsequent post‐plasma treatment processes. However, we maintained the presence of N2O plasma and analyzed its effect on device performance and reliability. While a‐IGZO TFTs fabricated with N2O plasmaremoved during the post‐process exhibited non‐ideal negative Vth shifts under PBTS, the devices fabricated with N2O plasma present during post‐processing showed superior electrical performance and reliability, avoiding the non‐ideal Vth shift phenomenon. This study shows that maintaining N2O plasma during the post‐process is an effective method for ensuring device reliability as well as improved performance of a‐IGZO TFTs in mass production.

Plasma‐Enhanced Chemical‐Vapor‐Deposited SiOx(Ny)/n‐type Polysilicon‐on‐Oxide‐Passivating Contacts in Industrial Back‐Contact Si Solar Cells

In this article, different in situ grown plasma‐enhanced chemical vapor deposition (PECVD)‐grown interfacial oxides for n‐type polysilicon‐passivating contacts are investigated. Herein, SiOx(Ny)/n‐type amorphous silicon stacks created from either N2O plasma or O2 plasma are applied to POLy‐silicon on Oxide interdigitated back‐contact (POLO IBC) solar cells using the structured deposition process through a glass mask to create the IBC layout. The impact of plasma exposure time for interfacial oxide growth on solar cell efficiencies is experimentally determined. In the POLO IBC cell results, it is shown that the PECVD oxides SiOxNy and SiOx with optimized plasma exposure time give similar maximum efficiencies of 23.8% and 23.7%, respectively. In these data, the feasibility to deposit a high‐quality in situ PECVD interfacial SiOx(Ny) layers for surface passivation and current transport of passivated contacts at the same time is demonstrated. For the SiOx/n‐type polysilicon stack, it is found that both plasma exposure time for interfacial oxide growth and polysilicon anneal temperature variations can lead to similar optimum of solar cell efficiencies. The current open‐circuit voltage losses due to metallization for the solar cells are analyzed and a realistic efficiency of 25.22% is calculated to achieve optimized POLO IBC solar cells applying the synergistic efficiency gain analysis on Quokka3 simulations.

P‐2: Investigation of high mobility crystalline IGO TFT with top‐gate structure for LCD display application

The present paper reports the study of electrical characteristics and bias temperature stress (BT) stability of crystalline Indium‐Gallium oxide (IGO) dual‐gate thin film transistor (TFT) with top‐gate structure. TFT with normalized Ion over 100εA and PBTS/NBTIS of 0.35/‐2.85V was successfully fabricated. By adjusting oxygen partial pressure (O2%) and substrate temperature, we can control the wet etching rate (WER) of as‐deposited IGO film. After post annealing, crystalline IGO containing In2O3 phase with preferred orientation of (222) has been formed. The TFT characteristics uniformity and BT stability were found to depend on parameters of gate insulator (GI) deposition and pre‐treatment before GI. Based on experimental results, we propose high GI deposition temperature associated with low N2O plasma treatment power as the optimal condition for industrial production of crystalline IGO TFT.

Understanding and mitigating resistive losses in fired passivating contacts: role of the interfaces and optimization of the thermal budget

This work presents a study of p-type passivating contacts based on SiCx formed via a rapid thermal processing (RTP) step, using conditions compatible with the firing used to sinter screen-printed metallization pastes in industry. The contributions of the two interfaces (wafer/contact and contact/metal) to the contact resistivity are first decorrelated, identifying tunnelling at the wafer interface as the main contribution. We then investigate the influence of the active dopant concentration on the contact resistivity and the SiCx sheet resistance and propose strategies to reduce both resistances by increasing the thermal budget applied during RTP. Lastly, we discuss potentials and limitations of implementing the investigated stacks as rear side contacts of p-type devices with localized metallization. We demonstrate that increasing the thermal budget during RTP can effectively mitigate resistive losses and enhance contact performance and we show that an oxide layer that can withstand high thermal budgets is the key factor for obtaining simultaneously high passivation quality and good electrical properties. We investigate three different oxide types grown by HNO3 immersion, UV-O3 exposure and N2O plasma oxidation. The latter is demonstrated to be a promising candidate for an application in devices fabricated with high RTP thermal budget.

Plasma treatment for chemical SiOx enables excellent passivation of p-type polysilicon passivating contact featuring the lowest J of ∼6 fA/cm2

We study the preparation of high-quality p-type tunnel oxide passivated contact (p-TOPCon) using plasma-enhanced chemical vapor deposition (PECVD) technology in this work. We propose to use different plasmas to treat the ultrathin SiOx to improve the passivation quality of p-TOPCon. Experimentally, we use the nitric acid oxidation (NAOS) SiOx as the precursor and use pure N2, pure H2, and N2O/H2 plasmas to treat the SiOx precursor layer. Three observations are found. 1) Pure H2 plasma treatment can improve the SiOx quality by increasing the Si4+ content, but the passivation quality is not improved because of the etching effect of H2 plasma and the reduction of SiOx thickness. 2) The pure N2O plasma can improve the passivation quality but increases the contact resistivity (ρc) because of the increase of the SiOx thickness. 3) The N2O/H2 plasma treatment improves the passivation quality more effectively than pure N2O plasma, and meanwhile, it also keeps the contact resistivity at an acceptable value for high-efficiency solar cells. We assume that the atomic H provides the energy to etch the weak and dangling bonds and make SiOx thinner, while the atomic O that makes SiOx thickness unchanged balances the etching effect of atomic H. With the optimized N2O/H2 plasma treatment, the passivation quality of p-TOPCon is improved, featuring the best implied open-circuit voltage (iVoc) of ∼732 mV and the lowest single-sided saturation current density (J0,s) of ∼6 fA/cm2 on the lifetime sample with the n-type silicon substrate and the AlOx/SiNx capping layer. These results demonstrate that the plasma treatment is a promising way to boost the passivation quality of PECVD p-TOPCon structures. Finally, as an example, we use numerical simulation to predict the performances of the solar cells integrating the p-TOPCon structure on the rear side of n-c-Si and demonstrate a 24.8% efficiency with the p-TOPCon whose SiOx is improved by the optimized plasma treatment.

Research on the β-Ga2O3 Schottky barrier diodes with oxygen-containing plasma treatment

This Letter reports two kinds of oxygen-containing plasma treated β-Ga2O3 Schottky barrier diodes (SBDs), including N2O plasma treatment and O2 plasma treatment, and the SBD without plasma is prepared for comparison. I–V characteristics, breakdown characteristics, and trap state characteristics of three devices have been studied. It is found that the turn-on voltage of SBDs with N2O plasma can reduce to 0.6 V, and the better current density of 750 A/cm2 and an on-resistance of 3.5 mΩ cm2 are obtained after the N2O plasma treatment. Moreover, the breakdown voltage of SBDs with N2O plasma is 50.2% higher than the conventional one, whose value reaches 323 V. In addition, the trap states' characteristics of the devices are studied, which show that the oxygen-containing plasma can reduce the deep level trap states density partly in the anode region, which can improve the surface quality effectively.

Study of hydrogenation with electron injection for TOPCon solar cells with different tunneling oxide layers

In order to further improve the photovoltaic conversion efficiency of tunnel oxide passivated contact (TOPCon) solar cells, the hydrogenation with electron injection (HEI) technique on TOPCon solar cells with different processes for preparing tunneling SiOx layers was investigated. The experimental results showed that the conversion efficiency enhancement of TOPCon solar cells with a tunneling SiOx layer prepared by a N2O plasma oxidation method (PO method) was lower than that of the cells prepared by an indirect thermal oxidation method (TO method) under the same HEI treatment conditions. Further studies proved that the improvement effect after HEI treatment was closely related to the denseness of the tunneling SiOx layer: HEI treatment for TOPCon solar cells with a low dense tunneling SiOx layer (TO method) requires higher temperature, higher current, and longer time to achieve a better improvement, while the HEI parameters of cells with a high dense tunneling oxide layer (PO method) need to be readjusted. By optimizing the HEI parameters for cells prepared by the PO method, the power conversion efficiency (PCE) of the cells was finally improved by 0.098%abs. The PCE was improved from the original negative growth to a level close to that of the TOPCon cells prepared by the TO method. This result provided an improved process flow to further increase the efficiency of TOPCon solar cells.

Rational design of oxide heterostructure InGaZnO/TiO2 for high-performance thin-film transistors

In this study, hetero-structured and self-passivated oxide thin film transistors (TFTs) were fabricated, wherein the channel comprised a N2O plasma (a-IGZO:N2O) treated a-IGZO front layer and TiO2 ultra-thin back layer. A high field-effect mobility (μFE) of 40.5 cm2/Vs and small sub-threshold swing (SS) of 250 mV/decade upon a SiO2/Si substrate were achieved using a rational design. Moreover, small threshold voltage shifts (ΔVth) of 0.5 (−0.7) and 0.8 (−0.9) V under gate bias and light illumination stress tests were obtained. Using Si3N4/HfO2 gate dielectrics, μFE and SS were enhanced to 53.6 cm2/Vs and 75 mV/decade, respectively. Experimental observations indicate that the electrons transfer from TiO2 to a-IGZO:N2O layer resulted in the accumulation of free carriers near a-IGZO:N2O/TiO2 interfaces. Additionally, an appropriate N2O treatment reduced the oxygen-related defects and bulk/interface trap density, while controlling the carrier density in the bilayer a-IGZO:N2O/TiO2 TFTs. Furthermore, the ultra-thin TiO2 layer acted as a surface passivation layer that reduced the leakage current and protected the channel from ambient influences. The proposed high-performance hetero-structured a-IGZO:N2O/TiO2 TFTs with superior stability are expected to provide a new and effective approach to obtaining high-performance metal oxide TFTs for application in thin film electronics.

P‐2: Nitrogen Behaviors in PEALD‐Grown SiO2 Films Using N2O Plasma Reactant and Its Application in ALD‐IZO TFTs

We studied nitrogen (N) behaviors in plasma‐enhanced atomic layer deposition (PEALD)‐grown silicon dioxide (SiO2) using nitrous oxide (N2O) plasma reactant. The gradually improved breakdown phenomenon is attributed to N contents. However, although increase in the N contents, excess plasma power is degraded electrical characteristics. For applications of the SiO2 films using N2O plasma reactant, we fabricated indium‐zinc oxide top‐gate thin film transistors with SiO2 gate insulator (G.I). The stable both transfer characteristics and instability results are originated from decrease in oxygen vacancy in active layer by N2O plasma treatment during the G.I deposition.

Impact of N2O Plasma Reactant on PEALD-SiO2 Insulator for Remarkably Reliable ALD-Oxide Semiconductor TFTs

We studied nitrogen (N) incorporation effects on the electrical characteristics of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> fabricated by plasma-enhanced atomic layer deposition (PEALD). To determine whether N could be incorporated into the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , nitrous oxide (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O) plasma with different plasma powers (100, 150, and 200 W) was used during the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> deposition, and the film properties were compared with SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> fabricated using a conventional oxygen (O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) plasma reactant. Compared to the O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> plasma reactant, the hard breakdown is improved by 27.5% as N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O plasma power increases up to 150 W, whereas it is degraded at a N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O plasma power of 200 W. These results are found to describe the relationship between the N content and film properties. The N content in the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films fabricated using increasing N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O plasma power of 100, 150, and 200 W gradually increased by 0.2%, 0.4%, and 0.5%, respectively. However, the N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O plasma power of 200 W results in increased O deficient Si bonding. To investigate the effects of continuous plasma exposure at the bottom layer during the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> deposition, we fabricated indium–zinc oxide (IZO) top-gate bottom-contact (TG-BC) thin-film transistors (TFTs) using the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as a gate insulator (G.I). Compared to the O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> plasma, the IZO TFTs using N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O plasma reactant during the G.I deposition show stable transfer characteristics. The IZO TFT using N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O plasma with 150-W power during the G.I deposition shows the optimal positive/negative bias temperature stress (P/NBTS) results, with the threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathbf {TH}}$ </tex-math></inline-formula> ) variations of 0.0 and −0.3 V, respectively.

Influence of N2O plasma treatment on PET-based flexible bending sensors with ZnO nanorod array cross-linked with interdigitated electrode structures

We present a highly sensitive bending sensor fabricated with hydrothermally grown zinc oxide nanorod (NR) arrays cross-linked with interdigitated electrode patterns on polyethylene terephthalate substrates. To examine the effects of microstructural change in NR arrays on the device characteristics, N2O plasma treatment (PT) was carried out for 3 and 6 min for the seed layers. Negative resistance change (ΔR) was obtained in the case of convex bending, while positive ΔR was measured under the concave bending from every device prepared under different PT conditions, which is due to the change in the number of cross-linkings between the NRs. The device with no PT condition showed the highest gauge factor of 196 at a bending strain of 1.75% in the convex direction.

N2O plasma treatment effect on reliability of p-GaN gate AlGaN/GaN HEMTs

This work investigates the effect of N2O plasma treatment on the reliability of p-GaN gate AlGaN/GaN high-electron-mobility transistors (HEMTs), specifically in the AlGaN drift region. The formation of a GaON/AlON compound layer on the AlGaN surface after N2O plasma treatment was confirmed by energy-dispersive x-ray spectroscopy mapping and x-ray photoelectron spectroscopy analysis. When a device is under highly stressed conditions, the compound layer reduces the number of negatively charged interface traps and protects the AlGaN surface by hindering the Ga-out diffusion. The high temperature reverse bias reliability test demonstrated that the N2O plasma treatment enhanced the reliability of p-GaN gate HEMTs by suppressing the degradation of the on-resistance from 18.7% to 9.0%, after being subjected to a high drain bias (VDS = 700 V) at 200 °C for 1000 s.

The effect of passivation-layer process to amorphous InGaZnO thin-film transistors using back-channel etch method

In this work, based on the channel damage caused by source/drain etching and passivation-layer deposition, the effects of the passivation-layer process on amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) devices were studied by combining experimental investigation with simulation verification. In terms of experimental exploration, it was found that the back-channel N2O plasma treatment had a significant impact on the performance of the device, which was difficult to control. Hence, to achieve a low cost, the entire back-channel process was directly carried out as two steps of SiO x passivation-layer deposition and final thermal annealing. In the aspect of simulation verification, the influence of the passivation-layer deposition radio-frequency (RF) power and the annealing effect on the internal mechanism of the device was studied based on a high-concentration doped defect density of states (DOS) model (doping level was N D = 1020 cm−3). The experimental results demonstrated that the high-performance of an a-IGZO TFT device can be achieved by adjusting the RF power of SiO x passivation-layer deposition. It was more important that annealing after passivation-layer deposition was a critical step in the manufacture of high-performance TFTs. The device exhibited the ideal performance after annealing under 1000 W RF power, with a threshold voltage of 5.65 V, a saturation mobility of 12.87 cm2 V−1s−1, a subthreshold swing of 0.88 V dec−1, and a current on-off ratio of 2.62 × 10°8. In addition, using the DOS model, it was found that the SiO x passivation-layer process had a significant impact on the DOS distribution and the carrier distribution in the channel, which in turn caused the threshold voltage to drift. At last, the high uniformity and stability of an a-IGZO TFTs array on glass were characterized.

Comparison of NH3 and N2O Plasma Treatments on Bi2O3 Sensing Membranes Applied in an Electrolyte-Insulator-Semiconductor Structure.

In this study, bismuth trioxide (Bi2O3) membranes in an electrolyte–insulator–semiconductor (EIS) structure were fabricated with pH sensing capability. To optimize the sensing performance, the membranes were treated with two types of plasma—NH3 and N2O. To investigate the material property improvements, multiple material characterizations were conducted. Material analysis results indicate that plasma treatments with appropriate time could enhance the crystallization, remove the silicate and facilitate crystallizations. Owing to the material optimizations, the pH sensing capability could be greatly boosted. NH3 or N2O plasma treated-Bi2O3 membranes could reach the pH sensitivity around 60 mV/pH and show promise for future biomedical applications.

High linearity AlGaN/GaN HEMT with double-V th coupling for millimeter-wave applications

We demonstrated an AlGaN/GaN high electron mobility transistor (HEMT) namely double-V th coupling HEMT (DVC-HEMT) fabricated by connecting different threshold voltage (V th) values including the slant recess element and planar element in parallel along the gate width with N2O plasma treatment on the gate region. The comparative studies of DVC-HEMT and Fin-like HEMT fabricated on the same wafer show significantly improved linearity of transconductance (G m) and radio frequency (RF) output signal characteristics in DVC-HEMT. The fabricated device shows the transconductance plateau larger than 7 V, which yields a flattened f T/f max-gate bias dependence. At the operating frequency of 30 GHz, the peak power-added efficiency (PAE) of 41% accompanied by the power density (P out) of 5.3 W/mm. Furthermore, the proposed architecture also features an exceptional linearity performance with 1-dB compression point (P 1 dB) of 28 dBm, whereas that of the Fin-like HEMT is 25.2 dBm. The device demonstrated in this article has great potential to be a new paradigm for millimeter-wave application where high linearity is essential.

Visible to near-infrared photodetector based on SnSe2/WSe2 heterojunction with potential application in artificial visual neuron

Two-dimensional (2d) transition-metal dichalcogenides (TMDCs) are promising candidate materials for developing next generation nano optoelectronic devices, due to their strong interaction with light. In addition, the free of surface dangling bonds makes it possible to stacking any different types of 2D TMDCs together to form heterojunctions with desirable band structures for various applications. However, most of the 2D TMDCs are bipolar or strong unipolar n-type doped, while very few of them show weak p-type doping, which severely affects the performance of the formed heterojunctions. In this work, we fabricated a SnSe2/WSe2 heterojunction of type II band alignment with a small bandgap of ∼0.1 eV, which is ideally for developing optoelectronic devices responsible to a broad light spectrum. N2O plasma treatment is applied to enhance the p-type doping of both WSe2 and SnSe2, which results in the increased on–off ratio of n-type SnSe2 by 50 times and the hole mobility of WSe2 by 527 times. The WSe2/SnSe2 heterostructure also achieves a decent performance as a p–n junction, which exhibits photo responsivity of 450 mA W−1 and 133 mA W−1 for 700 nm visible light and 1600 nm infrared light, respectively, without any gate or source-drain bias, showing great photovoltaic effect. Moreover, the heterojunction shows great promise as an artificial visual neuron, which can differentiate the dark, visible and infrared light illumination conditions by applying a series of electrical pulses through the back-gate electrode.

Effects of Seed-Layer N2O Plasma Treatment on ZnO Nanorod Based Ultraviolet Photodetectors: Experimental Investigation with Two Different Device Structures.

The crystalline quality of ZnO NR (nanorod) as a sensing material for visible blind ultraviolet PDs (photodetectors) critically depends on the SL (seed layer) material of properties, which is a key to high-quality nanocrystallite growth, more so than the synthesis method. In this study, we fabricated two different device structures of a gateless AlGaN/GaN HEMT (high electron mobility transistor) and a photoconductive PD structure with an IDE (interdigitated electrode) pattern implemented on a PET (polyethylene terephthalate) flexible substrate, and investigated the impact on device performance through the SL N2O plasma treatment. In case of HEMT-based PD, the highest current on-off ratio (~7) and spectral responsivity R (~1.5 × 105 A/W) were obtained from the treatment for 6 min, whereas the IDE pattern-based PD showed the best performance (on-off ratio = ~44, R = ~69 A/W) from the treatment for 3 min and above, during which a significant etch damage on PET substrates was produced. This improvement in device performance was due to the enhancement in NR crystalline quality as revealed by our X-ray diffraction, photoluminescence, and microanalysis.

Modulation of MoTe2/MoS2 van der Waals heterojunctions for multifunctional devices using N2O plasma with an opposite doping effect.

van der Waals layered heterojunctions have a variety of band offsets that open up possibilities for a wide range of novel and multifunctional devices. However, due to their poor pristine carrier concentrations and limited band modulation methods, multifunctional p-n heterojunctions are very difficult to achieve. In this report, we developed a highly effective N2O plasma process to treat MoTe2/MoS2 heterojunctions. This allowed us to adjust the hole and electron concentrations in the two materials independently and simultaneously. More importantly, for the first time, we were able to create opposite doping on the two sides of the junction through a single-step treatment. With a very wide doping range from pristine to degenerate levels, a MoTe2/MoS2 heterojunction can be modulated to behave as a forward rectifying diode with enhanced rectifying ratio and as a tunneling transistor with negative differential resistance at room temperature. The new approach provides an effective and generic doping scheme for heterojunctions to construct versatile and multifunctional electronic devices.

Enhancement in the photonic response of ZnO nanorod-gated AlGaN/GaN HEMTs with N2O plasma treatment.

We demonstrate an improvement in the photoresponse characteristics of ultraviolet (UV) photodetectors (PDs) using the N2O plasma-treated ZnO nanorod (NR) gated AlGaN/GaN high electron mobility transistor (HEMT) structure. The PDs fabricated with ZnO NRs plasma-treated for 6 min show superior performance in terms of responsivity (∼1.54×10 5 A/W), specific detectivity (∼ 4.7×1013 cm·Hz-1/2/W), and on/off current ratio (∼40). These improved performance parameters are the best among those from HEMT-based PDs reported to date. Photoluminescence analysis shows a significant enhancement in near band edge emission due to the effective suppression of native defects near the surface of ZnO NRs after plasma treatment. As our X-ray photoelectron spectroscopy reveals a very high O/Zn ratio of ∼0.96 from the NR samples plasma-treated for 6 min, the N2O plasma radicals also show a clear impact on ZnO stoichiometry. From our X-ray diffraction analysis, the plasma-treated ZnO NRs show much greater improvement in (002) peak intensity and degree of (002) orientation (∼0.996) than those of as-grown NRs. This significant enhancement in (002) degree of orientation and stoichiometry in ZnO nano-crystals contribute to the enhancement in photoresponse characteristics of the PDs.