Remote-plasma-enhanced Metalorganic Chemical Vapor Deposition Research Articles

Low temperature epitaxial technology for GaN-based materials

<p indent="0mm">The band gap of GaN-based semiconductor materials covers the entire visible light band and has excellent physical and chemical properties, which makes it widely used in the fabrication of optoelectronic devices, power electronic devices, and radio frequency and microwave devices. Traditional GaN-based materials are usually epitaxially grown on high-temperature-resistant single-crystalline substrates such as sapphire, silicon, or silicon carbide using metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or hydride vapor phase epitaxy (HVPE). These epitaxial techniques usually use high temperature to crack the precursors involved in the reaction. With the deepening of informatization and intelligentization, the common demands for low-cost and flexibility of opto(electronic) devices have emerged. On one hand, the display technology is a key link to realize information exchange and intelligence. Moving towards an intelligent society requires further reduction of the display cost per unit area. At the same time, the wearable and portable flexible display technology also has broad application prospects. In addition, solid-state lighting has gradually penetrated into every corner of human life with the improvement of device performance. The application scenarios are rich and colorful. Judging from this, low-cost surface light sources will be a strong competitor for the next generation of lighting technology routes. On the other hand, reducing the fabrication cost of electronic devices per unit area also needs more attention in the future. For example, flexible electronic skin has broad and huge application prospects in artificial limbs, robotics, medical detection and diagnosis, etc., which has also spawned the demand for low-cost flexible sensors. It can be seen that the common requirements of the above applications for core components are low cost and flexibility, which is also one of the main development directions of the next generation of (opto)electronic devices. Amorphous substrates (such as glass, plastic, metal, polyethylene terephthalate (PET), polydimethylsiloxane (PDMS), etc.) that are cheap and easy to fabricate are ideal choices, but a significant disadvantage is that amorphous substrates cannot withstand high growth temperatures. Therefore, the need for low-temperature epitaxy of GaN-based materials has arisen, that is, a kind of epitaxy equipment that can use external electric field energy to crack the reaction precursor at low temperatures. So far, a variety of low-temperature epitaxial technologies have been developed based on the physical vapor deposition (PVD) and the chemical vapor deposition (CVD), and preliminary research results have been obtained. The PVD techniques include reactive magnetron sputtering, plasma-assisted MBE (PA-MBE), pulsed laser deposition (PLD), pulsed sputtering deposition (PSD), laser MBE (LMBE), etc. The CVD techniques include remote plasma CVD (RPCVD), migration enhanced afterglow CVD (MEA-CVD), remote plasma-enhanced MOCVD (RPEMOCVD), radical-enhanced MOCVD (REMOCVD), electron cyclotron resonance plasma-enhanced MOCVD (ECR-PEMOCVD), inductive coupled plasma MOCVD (ICP-MOCVD), etc. In this paper, the two types of low-temperature epitaxial technologies are introduced in detail, including the device structure, working conditions and related epitaxial growth results, and the characteristics of each type of technology are summarized. Finally, the development prospect of low temperature epitaxial technologies is prospected, and the focus of future research is pointed out. We hope this work can provide a useful reference for the low temperature epitaxy research of GaN-based materials.

Wurtzite Zn1−y(MgxCd1−x)yO quaternary systems for photodiodes in visible spectral range

We investigated the optical bandgap engineering of ZnO based quaternary alloy films of wurtzite Zn1−y(MgxCd1−x)yO for photodiodes in visible spectral range. Quaternary alloy films were successfully synthesized by remote-plasma enhanced metalorganic chemical vapor deposition (RPE-MOCVD). The wurtzite alloy system has an optical bandgap energy between 2.16eV and 3.25eV, which was controlled by the flow ratio of metalorganic sources. The crystal structure and composition was analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). This revealed that carrier compensation effects by alloying with MgO in Zn1−xCdxO system decreases carrier concentration. Strong compensation effects were observed in the bandgap range of Zn1−y(MgxCd1−x)yO between 3.0eV to 3.25eV and the carrier concentration decreased to 1015–1018cm−3. Schottky diodes of PEDOT: PSS/Zn1−y(MgxCd1−y)yO with optical bandgaps in the visible spectral range were fabricated to confirm the viability of photovoltaic applications. The diodes performed photovoltaic characteristics under a Xe–Hg lamp illumination through Schottky junctions. The photoresponse spectra showed a photosensitivity with cutoff energy of 2.23eV and peak energy of 2.90eV at 0V biasing.

Synthesis and characterization of N, In co-doped MgZnO films using remote-plasma-enhanced metalorganic chemical vapor deposition

We report the synthesis and characterization of MgZnO films co-doped with N and In using remote-plasma-enhanced metalorganic chemical vapor deposition (RPE-MOCVD). X-ray diffraction (XRD) analysis revealed the hexagonal wurtzite structure of the films. The film quality gradually degrades with increasing In content (y) and also with annealing at 800°C for 1min. A bandgap narrowing of 50meV was observed for N, In co-doped MgZnO film with an In content y=0.52% compared to N-doped MgZnO, which indicated the formation of a shallow N-acceptor band. Both N-doped MgZnO and N, In co-doped MgZnO films showed p-type conductivity. The N, In co-doped MgZnO films showed higher hole concentration and lower resistivity compared to N-doped MgZnO. A p-type conductivity with a high hole concentration of 7.8×1017–3.6×1018cm−3, low resistivity of 15–16Ωcm, and mobility of 0.11–0.5cm2/Vs was achieved for four different measurements of N, In co-doped MgZnO film with In content y=0.52%. The N-doped MgZnO film annealed at 800°C for 1min showed an increase of hole concentration and decrease of resistivity compared to as-grown film. However, the transformation of conduction type from p-type to n-type was observed for N, In co-doped MgZnO films with annealing at 800°C for 1min.

Indium-Doped MgxZn1-xO Films for ZnO-Based Heterojunction Diodes

Indium-doped MgxZn1-xO (MgxZn1-xO:In) thin film and ZnO:In thin films were successfully grown by remote plasma-enhanced metalorganic chemical vapor deposition (RPE-MOCVD). The In supply source used is trimethylindium (TMIn). The surface morphology, structural changes, and optical band gap energy in MgxZn1-xO:In were investigated by varying the amount of the supplied TMIn and were compared with ZnO:In systems. Our main achievement point is that we have markedly improved the surface morphology of Mg0.05Zn0.95O:In films from being pillar like to being film like with an increase in the amount of indium. The improved green electoluminescence emission (EL) characteristic the ZnO-based DH system was employing the Mg0.05Zn0.95O:In film here and in conclusions.

Red Emission from ZnO-Based Double Heterojunction Diode

We have successfully realized high-quality red-band-gap Zn1-xCdxO films by remote-plasma-enhanced metalorganic chemical vapor deposition (RPE-MOCVD). By using the in-situ thermal annealing process, the compositional homogeneity of the Zn1-xCdxO films has been markedly improved. Proper annealing in vacuum provides a full-width at half-maximum (FWHM) in photoluminescence (PL) of 126 meV, which is almost comparable to that of typical ZnO films. ZnO-based double heterojunction (DH) system with in-situ post-annealed Zn1-xCdxO film is grown on p-4H-SiC substrate, which shows red electroluminescence (EL) with improved PL FWHM of 213 meV.

Dot-Height Dependence of Photoluminescence from ZnO Quantum Dots

We report on the optical properties of ZnO nanodots and how they are influenced by the height of the dot configuration. The nanodots were grown on SiO2/Si substrates by remote-plasma enhanced metalorganic chemical vapor deposition (RPE-MOCVD). The dot configuration was regulated by controlling the growth time. The photoluminescence (PL) spectra of nanodots having average dot height of 2.5, 3.5, and 4.5 nm grown on SiO2/Si substrates were measured at 16 K. A blue shift in the excitonic emission was observed for shorter dots due to a larger quantum confinement effect. The fractional-dimensional space model was used to estimate a dimensionality of 2.35 for ZnO nano dots with an average dot height of 2.5 nm.

Optical Properties of Wurtzite Zn1-xCdxO Films Grown by Remote-Plasma-Enhanced Metalorganic Chemical Vapor Deposition

Zn1-xCdxO films were grown on a-plane (1120) sapphires by remote-plasma-enhanced metalorganic chemical vapor deposition (RPE-MOCVD). The growth temperature, the group-II flow ratio R, and RF power are important parameters for the growth of Zn1-xCdxO films by RPE-MOCVD. R is defined as the molar function of [DMCd/(DEZn+DMCd)]. We discuss typical growth features associated with RPE-MOCVD and the refractive indices of wurtzite-type films. The band gap energy of Zn1-xCdxO grown at 350 °C can be controlled from 3.3 down to 1.8 eV. The refractive index is measured by ellipsometry at 1.96 eV and is found to vary from 2.07 to 2.78.

P-type nitrogen-doped ZnO thin films on sapphire [formula omitted] substrates by remote-plasma-enhanced metalorganic chemical vapor deposition

Nitrogen doped ZnO films were successfully grown, by remote-plasma-enhanced metalorganic chemical vapor deposition (RPE-MOCVD), having p-type conduction with carrier concentration ranging from 10 13 to 10 15 cm −3 and resistivity of the order of 10 −1–10 2 Ω cm. ZnO and ZnO:N films on sapphire substrate were characterized by Fourier transform infrared (FT-IR) and Raman spectroscopy (RS). Nitrogen-related RS modes emerged at 289, 587 and 653 cm −1. Application of FT-IR for characterization, specially for films (ZnO and ZnO:N) deposited on a-plane sapphire was used as a new concept. IR modes of carbon–nitrogen complexes (CN, CC, and CO), NO and OH were observed. The complexes created in as-grown films were weakened due to annealing leading to change in conductivity to p-type. ZnO:N/ZnO (p–n) junctions were fabricated and rectifying I–V characteristics were obtained confirming attainment of p-type conduction.

Mg xZn 1−xO films grown by remote-plasma-enhanced MOCVD with EtCp 2Mg

Mg x Zn 1− x O films were successfully grown by remote-plasma-enhanced metalorganic chemical vapor deposition (RPE-MOCVD) with bis-ethylcyclopentadienyl magnesium (EtCp 2Mg). Mg content x in Mg x Zn 1− x O films was controlled by varying the growth temperature and the radio-frequency (RF) power. The Mg content x in wurtzite-Mg x Zn 1− x O films slightly increased around 0.07 with increasing the growth temperature from 400 to 600 °C. At 700 °C, Mg x Zn 1− x O films had wurtzite and rock-salt structure, and Mg content increased to 0.42. Mg content x in wurtzite-Mg x Zn 1− x O films decreased from 0.25 to 0.09 with increasing RF power from 20 to 70 W. And Mg x Zn 1− x O films grown between 0 and 10 W had amorphous structure.

Characterization of MgxZn1-xO Films Grown by Remote-Plasma-Enhanced Metalorganic Chemical Vapor-Deposition using bis-Ethylcyclopentadienyl Magnesium

MgxZn1-xO films were successfully grown on a-plane sapphire (112̄0) substrates by remote-plasma-enhanced metalorganic chemical vapor-deposition (RPE-MOCVD) using diethyl zinc (DEZn) and bis-ethylcyclopentadienyl magnesium (EtCp2Mg). By increasing magnesium content in the films, the crystal structure was shifted through a mixed state from wurtzite to rock salt. The optical band-gap of the films at nearly 3.28 eV was shifted to 3.69 eV by alloying with magnesium depending on the alloy composition. Both optical absorption edges and emission peaks of MgxZn1-xO films shifted to higher energy when the magnesium content at room temperature was increased, showing alloy broadening. The Stokes' shift of wurtzite MgxZn1-xO alloy films was quantitatively evaluated. The results are relevant to exciton localization.

Growth of Mg xZn 1 − xO films using remote plasma MOCVD

Mg x Zn 1 − x O films were successfully grown on a-plane sapphire ( 1 1 2 ¯ 0 ) substrates by remote plasma enhanced metalorganic chemical vapor deposition (RPE-MOCVD). Diethyl zinc (DEZn), bis-ethylcyclopentadienyl magnesium (EtCp 2Mg) and oxygen plasma were used as source materials. By increasing Mg content in the films, the crystal structure was shifted through a mixed state from wurtzite to rock-salt with no significant segregation. Both optical absorption edges and emission peaks of Mg x Zn 1 − x O films shifted to the higher energy by increasing the Mg content at room temperature, showing an alloy broadening. The Stokes’ shift of wurtzite Mg x Zn 1 − x O alloy films was quantitatively evaluated, resulting in a linear dependence on the absorption edge energy.

Growth and characterization of Zn 1− xCd xO films using remote plasma MOCVD

Zn 1− x Cd x O films were successfully grown by remote plasma enhanced metalorganic chemical vapor deposition (RPE-MOCVD) with diethyl zinc, dimethyl cadmium, and oxygen plasma. The Cd composition x in the Zn 1− x Cd x O films was tuned by changing a flow rate of group-II sources. With increasing the Cd composition x, the crystal structure was changed from wurzite (WZ) to rock-salt (RS). The optical band-gap of the Zn 1− x Cd x O films with the wurzite structure up to x ≤ 0.7 varied from 3.3 eV down to 1.9 eV.

Hydroxyl-Radical-Assisted Growth of ZnO Films by Remote Plasma Metal-Organic Chemical Vapor Deposition

The hydroxyl-radical-assisted growth of ZnO films by remote plasma-enhanced metal-organic chemical vapor deposition (RPE-MOCVD) was investigated. Plasma was generated by an RF discharge in O2. The change of the carrier gas from N2 to H2 resulted in a significant increase in deposition rate. It was found from the spectroscopic characterization of light emitted by the reactor gas in the vicinity of a substrate that the effect of the carrier gas on deposition rate is related to the occurrence of OH radicals. Oxygen radicals and OH radicals, which were observed by spectroscopic measurement, promoted film growth and suppressed deep-level emissions in photoluminescence spectra. To elucidate the effects of O and OH radicals, hydrogen and helium remote plasma techniques were also used in film growth for comparison. Finally, the ZnO films fabricated by the OH radical-assisted growth were investigated by photoluminescence and X-ray diffraction (XRD) analyses. In addition, the Zn-termination effects of the sapphire substrate surface on heteroepitaxial ZnO film growth weres investigated.

The Structure of Plasma-Deposited and Annealed Pseudo-Binary ZrO2-SiO2 Alloys

ABSTRACTThe internal structures of various (ZrO2)x(SiO2)1-x alloys (x ≤ 0.5) were investigated. A remote plasma enhanced-metal organic chemical vapor deposition (RPEMOCVD) process was used to deposit films with varying alloy composition on Si(100) substrates. This study indicates that for the glassy silicate phase, g-ZrSiO4, a glass transition temperature, Tg, exists between 800°C and 900°C at which phase separation into the end-member components, SiO2 and ZrO2, occurs.

Effect of Hydrogen on GaN Growth by Remote Plasma-Enhanced Metal-Organic Chemical Vapor Deposition

The effects of hydrogen on GaN growth by remote plasma-enhanced metal-organic chemical vapor deposition (RPE-MOCVD) were investigated. Hydrogen addition changed the gas-phase reaction in the plasma and resulted in a Ga excess growth condition by scavenging activated nitrogen species, resulting in decreased carbon incorporation in Ga-sites. Furthermore, the GaN layer had a smooth surface with Ga polarity, whereas the layer grown without hydrogen addition showed a facetted surface with N polarity.

Remote Plasma Enhanced-Metal Organic Chemical Vapor Deposition of Zirconium Oxide/Silicon Oxide Alloy, (ZrO2)1-(SiO2)1−x (x:≤0.5), Thin Films for Advanced High-K Gate Dielectrics

ABSTRACTA remote plasma enhanced-metal organic chemical vapor deposition (RPE-MOCVD) process was developed for the preparation of non-crystalline (ZrO2)x-(SiO2)1−x (x ≤ 0.5) alloys, targeting the compound composition ZrSiO4with k ∼ 12.5. Shifts in Si LVV and Zr LMM AES energies with respect to elemental values showed that the deposited film was a fully-oxidized zirconium/silicon alloy. FTIR results were consistent with AES, and a Zr-O-Si bonding mode was identified in the spectra. The films were amorphous before and after RTA at 900°C for 30 sec, as monitored via RHEED. Optical absorption measurements indicated the onset of band-to-band transitions at an energy of approximately 6 eV. Finally, C-V testing showed that the films were insulating.

ZnTe epitaxial growth by remote plasma enhanced metal organic chemical vapor deposition

Zinctelluride (ZnTe) layers have been grown epitaxially on GaAs (100) substrates by a remote plasma enhanced metal organic chemical vapor deposition (RPE-MOCVD). Diethylzinc and diethyltellurium are used as source materials and hydrogen radicals generated by rf plasma are introduced into the reaction chamber for the film formation. It has been found that the growth rate increases extensively in the presence of hydrogen radicals and epitaxial growth of ZnTe can only be achieved with enough hydrogen radicals. The film formation is not observed if the deposition is carried out without H radicals and with N radicals. P-type ZnTe films are obtained when a mixture gas of H 2 and N 2 or NH 3 is used for the plasma. The resistivity and carrier concentration of ZnTe films are evaluated as 1.98×10 −2 Ω cm and 1.6×10 19 cm −3, respectively. These results clearly suggest that hydrogen radicals are indispensable for ZnTe growth in the MOCVD system.

Preparation of Heavily N-Type ZnSe Doped by Iodine in Remote Plasma Enhanced Metal Organic Chemical Vapor Deposition

Iodine-doped zinc selenide (ZnSe:I) layers were grown by remote plasma enhanced metal organic chemical vapor deposition (RPE-MOCVD) using n-butyliodide (n-BtI). The carrier concentration was controlled from 2×1016 to 8.2×1019 cm-3 by the dopant flow rate, where the mobilities renged from 200 to 50 cm2 V-1 s-1, respectively. The low-resistivity of 7.3×10-4 Ω cm was attained at the highest doping level.

Single molecular precursor metal-organic chemical vapor deposition of MgAl2O4 thin films

MgAl2O4 films have been grown epitaxially on both Si(100) and MgO(100) by a novel single source metal-organic chemical vapor deposition (MOCVD) process. A single molecular source reagent [magnesium dialuminum isopropoxide, MgAl2(OC3H7)8] having the desired Mg: Al ratio was dissolved in a liquid solution and flash-vaporized into the reactor. Both thermal and plasma-enhanced MOCVD were used to grow epitaxial MgAl2O4 thin films. The Mg: Al ratio in the deposited films was the same as that of the starting compound (Mg: Al = 1:2) over a wide range of deposition conditions. The deposition temperature required for the formation of crystalline spinel was found to be significantly reduced and crystallinity was much improved on Si by using a remote plasma-enhanced MOCVD process. The epitaxial nature of the MgAl2O4 films was established by x-ray pole figure analysis.