Compound-source Molecular Beam Epitaxy Research Articles

Preparation of europium‐doped GaN and AlGaN films grown by radical‐nitrogen‐assisted compound‐source MBE

AbstractBy the compound‐source molecular beam epitaxy (CS‐MBE), GaN:Eu and AlGaN films grown on both Al2O3(0001) and GaAs(100) substrates were prepared. Under RHEED observation, streak RHEED patterns from GaN were observed. This result shows that the surface of the film grown by CS‐MBE is atomically flat. From the XRD measurements, for GaN:Eu/Al2O3(0001), the film was oriented to c‐axis. On the other hands, for GaN:Eu/GaAs(100), the layer includes both the hexagonal and cubic phases. From the PL measurements, the PL spectra of both GaN:Eu/Al2O3 and GaN:Eu/GaAs(100) showed PL peaks related to Eu3+ ion. For GaN:Eu/GaAs(100), it is possible that part of Eu atom incorporates cubic‐GaN site (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

GaN growth on (111)Al substrates by CS‐MBE and their chemical lift‐off technique

AbstractThe low‐temperature growth of GaN on (0001) sapphire and (111)Al substrates by compound‐source molecular beam epitaxy (CS‐MBE) with was investigated. Although precise control of the V/III ratio was required for the growth, the near‐bandedge‐emission (NBE)‐dominant photoluminescence spectra of hexagonal GaN layers were observed at RT. The GaN layers were also grown on aluminum substrates with and without nitridation by CS‐MBE. Reflection high‐energy electron diffraction patterns of the layers indicate that the nitridation is effective for GaN growth by CS‐MBE on aluminum substrates. For further improvement of the GaN crystalline quality, the use of epitaxially grown Al layers as the substrates for the growth was proposed. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Pseudomorphic growth and strain relaxation of α-Zn3P2 on GaAs(001) by molecular beam epitaxy

Tetragonal zinc phosphide (α-Zn3P2) was grown pseudomorphically, by compound-source molecular-beam epitaxy on GaAs(001). The films grew coherently strained, with epitaxial relationships of Zn3P2(004)‖GaAs(002) and Zn3P2(202)‖GaAs(111). Partial relaxation of the Zn3P2 lattice was observed for films that were >150nm in thickness. Van der Pauw and Hall effect measurements indicated that the films were intrinsically p-type, presumably due to the incorporation of phosphorus interstitials. The carrier mobilities in strained films (>40cm2V−1s−1) were comparable to the carrier mobilities that have been reported for bulk Zn3P2 single crystals. The carrier densities and mobilities of holes decreased significantly upon film relaxation, consistent with the evolution of compensating dislocations.

Nitridation of (1 1 1)Al substrates for GaN growth by molecular beam epitaxy

The GaN layers were grown by compound-source molecular beam epitaxy (CS-MBE) on (1 1 1) aluminum (Al) substrates with and without nitridation. The melting point of Al substrates limits the growth temperature. The layers were grown at 650 °C. Reflection high-energy electron diffraction (RHEED) patterns of the layers indicate that the nitridation is effective for GaN growth by CS-MBE on aluminum substrates. Photoluminescence was observed from the layer grown on the Al substrate with nitridation at RT.

Fabrication of AlN films at low temperature by CS‐MBE technique

AbstractThe low‐temperature deposition of AlN films by compound‐source molecular‐beam epitaxy (CS‐MBE) technique was studied. AlN powder was used as the source and no additional nitrogen source was introduced during the deposition. X‐ray photoelectron spectroscopy (XPS) results show that Al‐N bonds were formed in the deposited films. It was clarified that the nitrogen atoms were supplied to the substrate from the AlN source and that the oxygen concentration in the deposited AlN films depended on the residual oxygen concentration in the AlN powder used as the source. The breakdown electric field of the AlN film was over 4.2 MV/cm, which indicates that the films deposited at a low temperature of less than 300 °C can be applied as the insulator in GaN‐based electroluminescent devices. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication of GaN‐based UV TF‐ELDs by CS‐MBE technique and their application to RGB light‐emitting pixels

AbstractGaN‐based thin‐film electroluminescence devices (TF‐ELDs) operating in the UV spectral region were fabricated on Al substrates. GaN films were deposited by compound‐source molecular beam epitaxy (CS‐MBE) technique. Red, green and blue (RGB) light‐emitting pixels were fabricated using the GaN‐based TF‐ELDs as excitation sources. The emission efficiencies of such TF‐ELDs were reported. The estimated luminances of the RGB emitters based on the GaN films were 0.2‐7 kcd/m2, which indicate that the GaN‐based TF‐ELDs have a potential for application in flat‐panel displays (FPDs). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Introduction of preheated ammonia during GaN growth on Si by compound-source MBE at low temperature

Preheated ammonia was introduced during GaN growth on Si by compound-source molecular-beam epitaxy (CS-MBE) at a low temperature. The use of preheated ammonia increased the surface smoothness and the intensity of cathodoluminescence (CL). Although the introduction of ammonia leads to the limited migration of the Ga surface atoms during the growth, the thermal energy supplied by the preheated ammonia assisted the surface migration. Furthermore, it was demonstrated that the introduction of preheated ammonia during the growth was effective for improving the CL intensity of the GaN layers at low temperatures. This is due to the reduction of the hydrogen concentration in the layers.

Low-temperature deposition of hexagonal GaN films for UV electroluminescent devices by CS-MBE technique

GaN-based electroluminescent devices (ELDs) operating in UV spectral region are proposed for the UV excitation source and their fabrication process using the compound-source molecular beam epitaxy (CS-MBE) technique. The trial substrates were (0 0 0 1)6H–SiC, Ta 2O 5/Al, and Ta 2O 5/glass substrates. In particular, the GaN buffer layer deposited at RT for the fabrication is discussed. The grown films were characterized by cathodoluminescence (CL), electroluminescence (EL), reflection high-energy electron diffraction (RHEED), and atomic force microscopy (AFM). The UV-light emission observed from the GaN-based ELDs fabricated using CS-MBE technique is demonstrated under operating conditions of 340 V at 200 Hz (pulsed wave). Red, green, and blue (RGB) pixels using phosphors (Y 2O 2S:Eu, BaMgAl 10O 17:Eu+Mn, BaMgAl 10O 17:Eu, respectively) were also demonstrated.

Fabrication of GaN‐based electroluminescent devices on Al substrates and their application to red, green and blue pixels for flat‐panel displays

GaN-based thin-film electroluminescent devices (TF-ELDs) operating in the UV spectral region were fabricated on Al substrates. GaN films were deposited by compound-source molecular beam epitaxy (CS-MBE) technique. During the deposition, the cell temperature of the GaN compound source is one of the key factors for reducing the excess Ga in the films. The UV light emission (peak wavelength 375 nm) corresponding to the near-band-edge emission of hexagonal GaN was observed from GaN-based TF-ELDs. Furthermore, red, green and blue (RGB) lighting pixels were fabricated using UV GaN-based TF-ELDs in combination with RGB phosphors. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Compound-source molecular beam epitaxy of GaN using GaN powder and ammonia as sources

Compound-source molecular beam epitaxy (CS-MBE) of GaN layers using GaN powder and ammonia as sources is discussed. In particular, the reduction of excess Ga in GaN layers by introducing ammonia supply is discussed on the basis of their refraction high-energy electron diffraction (RHEED) patterns, X-ray photoelectron spectroscopy (XPS) spectra and atomic force microscopy (AFM) images. It was clarified that the ammonia supply is effective for the high growth rate of GaN layers and for the reduction of their oxygen concentration. During the growth, the surface migration of Ga atoms is limited by the ammonia supply.

Photoluminescence spectra of GaN films grown at low temperature by compound‐source molecular beam epitaxy

AbstractThe photoluminescence spectra of GaN films deposited by compound‐source molecular beam epitaxy (CS‐MBE) at 450 °C are reported. A near band‐edge emission was observed from the GaN layers grown on (0001) 6H‐SiC substartes by CS‐MBE at 18 K. The cathodoluminescence spectra of the deposited films and GaN powders were also observed at 20 K. The emission intensity per film thickness of the deposited films is roughly the same as that of GaN powders. Electroluminescent devices were fabricated using the deposited films, and a UV light emission was observed from these devices. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Compound-source Molecular Beam Epitaxy of GaN on Si at Low Temperature Using GaN Powder and Ammonia as Sources

ABSTRACTLow-temperature growth of GaN is very attracting for the application to light emitting devices grown on Si substrates because it prevents the melt-back reaction between Ga and Si substrates. The low-temperature growth of GaN by compound-source molecular beam epitaxy (CS-MBE) has been reported. In the previous report, GaN powders were used as a source and no additional nitrogen source was introduced during the growth. At present, its growth mechanism is unclear. In this paper, CS-MBE of GaN layers using GaN and ammonia as sources is discussed. Especially, the reduction of excess Ga in GaN layers by introducing ammonia supply is discussed based on their refraction high-energy electron diffraction (RHEED) patterns and x-ray photoelectron spectroscopy (XPS) spectra.

Relationship between Excess Ga and Residual Oxides in Amorphous GaN Films Deposited by Compound Source Molecular Beam Epitaxy

Amorphous GaN (a-GaN) films were deposited at a low temperature below 500°C by compound-source molecular beam epitaxy (CS-MBE). The relationship between excess Ga and its oxidation in the deposited GaN films is reported. X-ray photoelectron spectroscopy (XPS) revealed that the excess Ga in deposited films was oxidized in the air and converted to gallium oxide. By increasing the substrate temperature, the total amount of gallium oxide in the deposited films decreased due to the reduction of the excess Ga. Cathodoluminescence (CL) intensity from the UV to the blue spectral regions increased with as the amount of gallium oxide in the deposited films decreased.

GaN films deposited at low temperature on (111)Si by compound-source molecular beam epitaxy technique

GaN films were deposited at the low temperature by compound-source molecular beam epitaxy technique. Structural ordering of the GaN films was investigated using x-ray photoelectron spectroscopy (XPS) and refractive high-energy electron diffraction (RHEED) techniques. XPS spectra show that excess Ga in the films was oxidized. The binding energy of Ga–N bonds in the deposited GaN film is almost equal to that in GaN crystals. On the other hand, the RHEED patterns of the films deposited on SiO2∕(111) indicate that the long-range tetrahedral ordering in deposited GaN is disappeared although those on (111) Si were streaky.

GaN‐based UV/blue electroluminescent devices deposited on Si at low temperature

GaN layers were grown on (111)Si substrates at 450 °C by compound source molecular beam epitaxy (CS-MBE). Streaky reflection high-energy electron diffraction (RHEED) patterns of the GaN layers were observed after the growth. The results indicate the growth of a hexagonal GaN crystal on a Si substrate and the effectiveness of CS-MBE in the fabrication of GaN layers at low temperature. GaN-based electroluminescent devices (ELDs) using CS-MBE were fabricated on the Si substrates. Purplish blue emission was observed from the ELDs under the AC operation. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Low-temperature growth of GaN layers on (0001)6H–SiC by compound source molecular beam epitaxy

The low-temperature growth of GaN is required to prevent cracks due to thermal expansion. The lower limit of the temperature of the GaN growth by compound source molecular beam epitaxy (CS-MBE) was estimated using the results of reflection high-energy electron diffraction and atomic force microscopy. The lower limit of the temperature of GaN growth by CS-MBE was investigated and found to be below 450 °C. The lower limit is due to the migration of atoms at the surface and the re-evaporation of excess Ga atoms.

Amorphous GaN‐Based Electroluminescent Devices Operating in UV Spectral Region

Amorphous GaN films were deposited using a compound-source molecular beam epitaxy technique. Electroluminescent devices were also fabricated using the deposited films. The devices were operated using sine wave voltage at room temperature. One of the emission peaks was located in the UV spectral region. The deposition rate was increased by introducing a small ammonia flow.

Deposition of Amorphous GaN by Compound Source Molecular Beam Epitaxy for Electroluminescent Devices

Amorphous GaN films were deposited using compound source MBE. GaN powder was used as the source material and no additional nitrogen sources were supplied. Although the N/Ga ratio in the layers deposited at temperatures lower than 400 °C was low, an increase of the substrate temperature improved the N/Ga ratio. The emission peaks of their photoluminescence spectra originated around the band edge of hexagonal GaN. Electroluminescent devices based on amorphous GaN were fabricated and were found to show UV emission. Amorphous GaN is one of the candidate materials for light-emitting devices operating in the UV to the blue spectral regions.

Molecular beam epitaxy growth and characterization of InGaP/InGaAs pseudomorphic high electron mobility transistors (HEMTs) having a channel layer over critical layer thickness

In/sub 0.5/Ga/sub 0.5/P/In/sub x/Ga/sub 1-x/As (x=0.33 and 0.40), pseudomorphic high electron mobility transistors (p-HEMTs) having a channel layer over the critical layer thickness were grown on patterned and nonpatterned GaAs substrates by using a compound-source molecular beam epitaxy (MBE). Characteristics of the highly strained InGaP/In/sub x/Ga/sub 1-x/As (x=0.33 and 0.40) p-HEMTs grown on patterned substrates were compared with those of conventional InGaP/In/sub 0.22/Ga/sub 0.78/As p-HEMTs grown on a nonpatterned substrate. The highly strained InGaP/In/sub 0.33/Ga/sub 0.67/As p-HEMT showed substantial improvements in device performances including DC (drain saturation current and transconductance), microwave (f/sub T/ and f/sub max/), low-frequency noise (Hooge parameter), and high-frequency noise (minimum noise figure and associated gain) characteristics compared with those of the conventional InGaP/In/sub 0.22/Ga/sub 0.78/As p-HEMT. The improvements in device performances of the highly strained InGaP/In/sub 0.33/Ga/sub 0.67/As p-HEMT are attributed to the improved transport property of the high-quality highly strained In/sub 0.33/Ga/sub 0.67/As channel layer achieved by the use of the patterned substrate growth. The results indicate the potential of highly strained InGaP/In/sub x/Ga/sub 1-x/As p-HEMTs having a channel layer in excess of the critical layer thickness grown on patterned GaAs substrates for use in high-performance microwave device applications.

Deposition of GaN Films on Glass Substrate and Its Application to UV Electroluminescent Devices

AbstractGaN films were deposited on glass substrates using a compound-source molecular beam epitaxy technique. Electroluminescent devices with a double-insulator structure were also fabricated using the deposited films. When the devices were operated using a sine-wave voltage, one of the emission peaks was located in the UV spectral region. Introducing a small ammonia flow increased the deposition rate.