Optimization of the GaN epilayer quality using in-situ reflectance measurements

2000 ◽  
Vol 639 ◽  
Author(s):  
Sandra Ruffenach-Clur ◽  
Matthieu Moret ◽  
Olivier Briot ◽  
Nathanaël Moreaud ◽  
Joseph Calas ◽  
...  
Keyword(s):  
Low Temperature ◽  
Growth Temperature ◽  
Layer Growth ◽  
Ex Situ ◽  
Nucleation Layer ◽  
Mocvd Growth ◽  
System A ◽  
Tremendous Amount ◽  
Temperature Deposition

ABSTRACTAlthough a tremendous amount of work has been done these last years on the nitride semiconductor system, a lot is still to be understood regarding the growth mechanisms of GaN. The standard GaN MOCVD growth process includes the low temperature deposition of a nucleation layer, followed by an anneal at high temperature, and the GaN layer is then deposited. The number of process parameters which can be used to tune the growth is very large (temperatures, times, thicknesses, molar flow rates and ratios …) and, due to the coupling between them, the role of each one is not clearly understood. In this paper, we present systematic series of growth experiments, where in-situ reflectance monitoring was used and correlated to ex-situ optical characterization of the samples by photoluminescence at low temperature (2K). Here, we demonstrate that the nucleation layer and its annealing have a determining effect. The nucleation layer growth temperature was not found to be a very sensitive parameter, while the amount of re-crystallization is. Surprisingly, the amount of ammonia present in the gas phase has a determining effect on the recrystallization behavior of the nucleation layer. Another interesting point is the sensitivity versus growth temperature for the main GaN layer, which was found to affect the initial stages of the growth in a drastic manner when changed by only 5°C. In-situ reflectance allowed us to tune precisely our process and to obtain GaN layers with 500 cm2/Vs electron mobility at room temperature and photoluminescence fwhm of 1.7 meV at 2K for the donor-bound exciton.

LP-MOCVD growth of GaAlN/GaN heterostructures on Silicon Carbide. Application to HEMT's devices.

2003 ◽  
Vol 798 ◽  
Author(s):  
M-A. di Forte Poisson ◽  
M. Magis ◽  
M. Tordjman ◽  
R. Aubry ◽  
M. Peschang ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Physical Properties ◽  
Defect Density ◽  
Growth Parameters ◽  
Substrate Surface ◽  
Surface Preparation ◽  
Layer Growth ◽  
Ex Situ ◽  
Nucleation Layer ◽  
Mocvd Growth

ABSTRACTThis paper reports on the LP-MOCVD growth optimisation of GaAlN/GaN heterostructures grown on Silicon Carbide substrates for HEMT applications, and on the first device performances obtained with these structures. The critical impact of some growth parameters on the physical properties of the GaAlN/GaN epilayers has been identified and studied using High Resolution X-Ray diffraction (HR-XRD), AFM, C-V and sonogauge measurements. The SiC substrate surface preparation (both ex-situ and in-situ) and the nucleation layer growth conditions (growth temperature, thickness, composition and strain) have been found to be key steps of the GaAlN/GaN/SiC growth process. SiC substrates from different suppliers have been evaluated and their influence on the physical properties of the GaAlN/GaN HEMT structures investigated. Static characteristics of the devices such as maximum drain current Idss or pinch-off voltage have been correlated with the nucleation layer composition of the HEMT structure and the defect density of the SiC substrate. First devices measured at 10 GHz using a load pull system exhibited CW output power in excess of 2.8 W/mm for a gate length of 0.5 μm. Under static measurements, we found an Idss around 1 A/mm and a pinch-off voltage of –5 V.

Role of boundaries in the crystallization of amorphous films

1988 ◽  
Vol 46 ◽  
pp. 626-627
Author(s):  
D. A. Smith
Keyword(s):  
Low Temperature ◽  
Amorphous State ◽  
Nucleation And Growth ◽  
Amorphous Films ◽  
Island Nucleation ◽  
Surface Steps ◽  
Transmission Electron ◽  
Component Systems ◽  
Temperature Deposition

The nucleation and growth processes which lead to the formation of a thin film are particularly amenable to investigation by transmission electron microscopy either in situ or subsequent to deposition. In situ studies have enabled the observation of island nucleation and growth, together with addition of atoms to surface steps. This paper is concerned with post-deposition crystallization of amorphous alloys. It will be argued that the processes occurring during low temperature deposition of one component systems are related but the evidence is mainly indirect. Amorphous films result when the deposition conditions such as low temperature or the presence of impurities (intentional or unintentional) preclude the atomic mobility necessary for crystallization. Representative examples of this behavior are CVD silicon grown below about 670°C, metalloids, such as antimony deposited at room temperature, binary alloys or compounds such as Cu-Ag or Cr O2, respectively. Elemental metals are not stable in the amorphous state.

scholarly journals Start-up Strategies for Anaerobic Ammonia Oxidation (Anammox) in In-Situ Nitrogen Removal from Polluted Groundwater in Rare Earth Mining Areas

2021 ◽  
Vol 13 (8) ◽  
pp. 4591
Author(s):  
Shuanglei Huang ◽  
Daishe Wu
Keyword(s):  
Rare Earth ◽  
Low Temperature ◽  
Removal Efficiency ◽  
Nitrogen Removal ◽  
Ex Situ ◽  
High Concentration ◽  
Low Concentration ◽  
Start Up ◽  
Anammox Activity

The tremendous input of ammonium and rare earth element (REE) ions released by the enormous consumption of (NH4)2SO4 in in situ leaching for ion-adsorption RE mining caused serious ground and surface water contamination. Anaerobic ammonium oxidation (anammox) was a sustainable in situ technology that can reduce this nitrogen pollution. In this research, in situ, semi in situ, and ex situ method of inoculation that included low-concentration (0.02 mg·L−1) and high-concentration (0.10 mg·L−1) lanthanum (La)(III) were adopted to explore effective start-up strategies for starting up anammox reactors seeded with activated sludge and anammox sludge. The reactors were refrigerated for 30 days at 4 °C to investigate the effects of La(III) during a period of low-temperature. The results showed that the in situ and semi in situ enrichment strategies with the addition of La(III) at a low-concentration La(III) addition (0.02 mg·L−1) reduced the length of time required to reactivate the sludge until it reached a state of stable anammox activity and high nitrogen removal efficiency by 60–71 days. The addition of La(III) promoted the formation of sludge floc with a compact structure that enabled it to resist the adverse effects of low temperature and so to maintain a high abundance of AnAOB and microbacterial community diversity of sludge during refrigeration period. The addition of La(III) at a high concentration caused the cellular percentage of AnAOB to decrease from 54.60 ± 6.19% to 17.35 ± 6.69% during the enrichment and reduced nitrogen removal efficiency to an unrecoverable level to post-refrigeration.

Electrical Evaluation of the Epi/Substrate Interface Quality after Different In-Situ and Ex-Situ Low-Temperature Pre-Epi Cleaning Methods

1998 ◽  
Vol 65-66 ◽  
pp. 237-240 ◽  
Author(s):  
Matty Caymax ◽  
S. Decoutere ◽  
Erika Röhr ◽  
W. Vandervorst ◽  
Marc M. Heyns ◽  
...  
Keyword(s):  
Low Temperature ◽  
Ex Situ ◽  
Interface Quality ◽  
Substrate Interface ◽  
Cleaning Methods

IONIZATION OF CHARGE-ANTICHARGE PAIRS IN ULTRATHIN PALLADIUM FILMS

1995 ◽  
Vol 09 (15) ◽  
pp. 939-946 ◽  
Author(s):  
YING LIU ◽  
JOHN C. PRICE
Keyword(s):  
Low Temperature ◽  
Electrical Conductance ◽  
Activation Energies ◽  
Arrhenius Behavior ◽  
Low Temperature Deposition ◽  
Temperature Deposition ◽  
A Charge

The electrical conductance and I–V characteristics of ultrathin Pd films prepared by low temperature deposition have been measured in situ. An Arrhenius behavior was found for the electrical conductance. A crossover between regimes with different activation energies was observed at a temperature TK. Below TK, the I–V characteristics of the film were found to be nonlinear. These observations are explained using a charge Kosterlitz-Thouless-Berezinskii transition picture which involves the ionization of charge-anticharge pairs.

The Effect Of The Nucleation Layer On The Low Temperature Growth Of Gan Using A Remote Plasma Enhanced – Ultrahigh Vacuum Chemical Vapor Deposition (RPE-UHVCVD)

1997 ◽  
Vol 482 ◽  
Author(s):  
Kyoung-Kook Kim ◽  
Dong-Jun Kim ◽  
Jong-Sik Paek ◽  
Je-Hee Jo ◽  
Hyo-Gun Kim ◽  
...  
Keyword(s):  
Chemical Vapor Deposition ◽  
Low Temperature ◽  
Growth Temperature ◽  
Vapor Deposition ◽  
Ultrahigh Vacuum ◽  
Chemical Vapor ◽  
Remote Plasma ◽  
Nucleation Layer ◽  
Temperature Growth ◽  
Low Temperature Growth

AbstractThis study investigated the low temperature growth of GaN on a nucleation layer in a remote plasma enhanced-ultrahigh vacuum chemical vapor deposition (RPE-UHVCVD) system which is equipped with an rf plasma cell for a nitrogen source. It was found that the growth temperature and the film thickness of the nucleation layer and the nitrogen flow rate for GaN growth play important roles in the improvement of crystallinity of the GaN layer. The nitridation of sapphire was also found to enhance the formation of facet shaped nuclei on the nucleation layer. As the temperature of the nucleation layer increased, islands with hexagonal and other facet shapes were formed on the grown GaN surface. This facet formation was related with the surface morphology and crystallinity of GaN. The best crystallinity was measured in a GaN layer with hexagonal facets on the surface and such GaN layers could be grown on a nucleation layer grown at 375 °C. Nitridation of sapphire and the growth temperature of the nucleation layer were also found to change the island shapes which enhances the formation of columnar structures in the GaN layer, resulting in the growth of a high crystalline GaN layer at low temperature.

In Situ Growth Studies of Artificial Layered (BA,SR,CA)CUO2 on Quasi-Ideal SrTiO3 Substrates by High Pressure Rheed

1999 ◽  
Vol 569 ◽  
Author(s):  
Gertjan Koster ◽  
Guus J.H.M. Rijnders ◽  
Dave H.A. Blank ◽  
Horst Rogalla
Keyword(s):  
High Pressure ◽  
Thin Film Deposition ◽  
High Energy ◽  
Layer Growth ◽  
Film Deposition ◽  
Perovskite Oxide ◽  
Ex Situ ◽  
Layer By Layer ◽  
Substrate Surfaces

ABSTRACTThe layered structure of oxides, like the high-T, cuprates, has been topic of research for some years now. The possibility to control thin film deposition on an atomic level has made fabrication of artificial structures and junctions accessible by depositing atomic layers or molecular blocks sequentially. Perfectly smooth substrate surfaces are hereby a prerequisite.Using Pulsed Laser Deposition (PLD), different perovskite oxide materials have been deposited on SrTiO3 substrates. With in situ high pressure Reflection High Energy Electron Diffraction we studied growth at different temperatures and oxygen pressures. Ex situ XRD and AFM have been used to study the morphology after deposition.Here we applied a new approach in obtaining layer-by-layer growth implied by the way of depositing the material, almost regardless of the deposition conditions. By alternating intervals of high supersaturation depositing one unit cell layer with intervals of lower supersaturation, one is able to force a layer-by-layer growth mode, which is in principle only feasible with PLD. We applied this technique to fabricate the layered infinite structure (Ba,Sr,Ca)CuO2 with artificial layered modulation, which have been characterized by XRD and AFM.

Optimization of SI-Wafer Cleaning and the use of Buffer-Layers for Epitaxial Growth of Sige-Layers by VLPCVD at T = 650 C

1992 ◽  
Vol 259 ◽  
Author(s):  
Matty R. Caymax ◽  
J. Poortmans ◽  
A. Van Ammel ◽  
W. Vandervorst ◽  
J. Vanhellemont ◽  
...  
Keyword(s):  
Low Temperature ◽  
Epitaxial Growth ◽  
Oxide Layer ◽  
Layer Growth ◽  
Buffer Layers ◽  
Ex Situ ◽  
Wafer Cleaning ◽  
Dry Etch ◽  
Water Rinse ◽  
Si Wafer

ABSTRACTFor low-temperature epi-growth in UHV-CVD-systems, the pre-epi, ex-situ cleaning of Si-wafers is known to be very critical. Various ways of etching the chemical oxide-layer after RCA-cleaning have been analysed by SIMS-measurements of the interfacial C, 0 and Bcontamination. Layer growth was performed at 650 C under a flow of 20 sccm of silane at 0.26 Pa. The best results (C and 0 below 2 % of a monolayer, and no detectable amounts of B) were obtained with “dry” etch-procedures, i.e. in which no water-rinse was applied after a normal 2 % HF-dip, or where 1F-vapour was used instead. Growth of Si1-xGex-layers with x < 0.1 succeeds quite well on such prepared substrates; for x between 0.1 and 0.25, we have found the use of a thin, pure Si-buffer layer (150 Å) to be indispensable. For x > 0.25, the growing layer can become quite rough, although this varies in time.

Improvement of Gaas Crystal Quality on Si Grown by Mocvd Through Two-Dimensional-Like Nucleation with Low Temperature in Situ Hydrogen/Arsine Plasma Cleaning

1990 ◽  
Vol 202 ◽  
Author(s):  
Euijoon Yoon ◽  
Rafael Reif
Keyword(s):  
Low Temperature ◽  
Buffer Layer ◽  
Crystal Quality ◽  
Ex Situ ◽  
Plasma Cleaning ◽  
Two Dimensional ◽  
Gaas Crystal ◽  
Hydrogen Atoms ◽  
Slow Kinetics

ABSTRACTWe report the significant improvement of GaAs crystal quality on Si grown by metal-organic chemical vapor deposition (MOCVD) with an in situ low temperature hydrogen/arsine plasma cleaning of the Si substrate at 450°C and a consequent controlled two-dimensional-like morphology of the low temperature buffer layer at its early stage. The most critical step that determines the interfacial cleanliness and the early stages of the nucleation and thin film formation of heteroepitaxial GaAs on Si in a non-ultrahigh vacuum MOCVD system is the substitution of hydrogen atoms passivating the Si surface after ex situ HF-dip with pas-sivating As atoms. Reduction of in situ cleaning temperature ensures the very slow kinetics of thermal desorption of the hydrogen atoms and re-oxidation of exposed Si surface from the reactor environment, and provides a fully As-passivated Si surface, leading to a 2D-like buffer layer.

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