Metalorganic Vapor Phase Epitaxy Growth Research Articles

Modeling and process design of III-nitride MOVPE at near-atmospheric pressure in close coupled showerhead and planetary reactors

The metalorganic vapor-phase epitaxy (MOVPE) growth of GaN from TMGa and NH 3 at higher process pressures up to near-atmospheric pressure in commercial production scale multi-wafer reactors is investigated. The Planetary Reactor ® and close coupled showerhead reactor are compared and their suitability for near-atmospheric pressure growth is demonstrated. Advanced model development and its validation by growth experiments are carried out with particular emphasis on gas phase reaction kinetics and nucleation dynamics. Both are recognized to be crucial for nitride MOVPE at elevated pressures. Process and reactor design improvements to enhance growth efficiency of GaN at elevated pressures are discussed and the physical origin of the pressure dependence of growth efficiency is analyzed. Model predictions and growth experiments are in good agreement.

MOVPE growth of Al xIn 1− xP using tertiarybutylphosphine in pure N 2 ambient

We have investigated metalorganic vapor phase epitaxy (MOVPE) growth of Al x In 1− x P alloy using tertiarybutylphosphine (TBP) as the phosphorus source in pure N 2 ambient. The effect of the substrate temperature on the aluminum composition of Al x In 1− x P epilayers during the MOVPE growth has been studied. When the source flow rates were kept unchanged, the aluminum composition of the Al x In 1− x P epilayer increased monotonically when the substrate temperature, T g, was raised from 580 °C to 660 °C during the growth. It became saturated when T g reached 660 °C and above. The crystalline quality of the grown Al x In 1− x P epilayers has been investigated by X-ray diffraction and photoluminescence measurements. A linear relationship between the aluminum composition of the Al x In 1− x P epilayer and TMAl/(TMAl + TMIn) source flow ratio has been obtained when grown at the optimized growth temperature of T g = 630 °C. It has also been observed that the aluminum incorporation coefficient of Al x In 1− x P epilayers decreased when the V/III source flow ratio was increased during the MOVPE growth.

Modeling of laser reflectance evolution during metalorganic vapor phase epitaxy growth of GaN using SiN treatment

We present the simulation of laser reflectance measurements performed during GaN growth by metalorganic vapor phase epitaxy (MOVPE). We used the scattering theory approximation to determine the root mean square (rms) surface roughness versus growth time. In the region of large roughness, the determined rms roughness exceeds the maximum value authorized by the Rayleigh criterion limiting the validity of the macroscopic roughness model. Another approach based on the effective medium approximation is used to simulate the entire reflectance signal evolution. An effective refractive index and growth rate profiles are determined.

Current status of large-area MOVPE growth of HgCdTe device heterostructures for infrared focal plane arrays

This paper reviews the current status of the growth of fully doped HgCdTe (MCT) devices by metalorganic vapor phase epitaxy (MOVPE). The current reactor system has been developed to produce 3-inch diameter epitaxial layers compatible with slice-scale processing. The new reactor system has achieved routine epitaxial growth of MCT with good morphology onto both gallium arsenide (GaAs) and GaAs on silicon (Si) wafers that were oriented (2–8°) off (100) orientation. The density of surface defects (so-called “hillocks”), typical of MOVPE growth on such orientation substrates, has been reduced to <5 cm−2 at a sufficient yield to make the production of low cluster defect 2D arrays possible. Alternative growth experiments onto cadmium telluride (CdTe) on Si substrates with (211)B orientation have also been performed to investigate their usefulness for infrared focal plane array (IRFPA) applications. Si substrates give better thermal expansion match to the read out Si circuits (ROIC). The horizontal reactor cell design has a graphite susceptor with a rotating platen capable of using substrates up to 4-inch diameter. Work, however, has concentrated on 3-inch diameter GaAs and GaAs on Si wafers substrates in the reactor, and these reproducibly demonstrated good compositional and thickness uniformity. Cut-off wavelength and thickness uniformity maps showed that there was sufficient uniformity to produce twelve sites of large format 2D arrays (640×512 diodes on 24-µm pitch) per slice. Minority carrier lifetimes in heterostructures is an important parameter and some factors affecting this are discussed, with special emphasis on As-doped material grown under various growth conditions in an attempt to reduce Shockley-Read (S-R) trap densities. New data are presented on trap densities and theoretical fitting of lifetimes in MOVPE material. Fully doped heterostructures have been grown to investigate the device performance in the 3–5 µm medium-wave IR (MWIR) band and 8–12 µm long-wave IR (LWIR). These layers have been fabricated into mesa arrays and then indium-bumped onto Si multiplexers. A summary of the 80-K device results shows that state-of-the-art device performance has been demonstrated in MOVPE-grown device structures.

MOVPE growth of InAsN films on GaAs(001) substrates with an InAs buffer layer

InAsN films of N content up to 3.5% without phase separation were grown on GaAs(001) substrates with a 1.9 μm-thick InAs buffer layer by metalorganic vapor phase epitaxy (MOVPE). In order to grow the InAsN films with a high N content at low temperature that assures a non-equilibrium growth environment, 1,1-dimetylhydrazine (DMHy) and tertiarybutylarsine (TBAs), which can be efficiently decomposed at low temperatures, were adopted as the N and As precursors, respectively. The electron concentration evaluated by the Hall measurement increased with increasing N content and the electrons were degenerated, while the fundamental absorption edge which was determined by the FT-IR absorption spectroscopy showed a blue-shift with increasing N content. These results indicate that the Burstein–Moss effect (or band filling effect) is dominant over the bandgap reduction expected from the bandgap bowing. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

MOVPE growth and optical characterization of GaAsN films with higher nitrogen concentrations

AbstractWe have successfully grown high‐N‐content GaAsN films up to 5.1% on GaAs(001) substrates using tertiarybutylarsine (TBAs) as the As precursor by metalorganic vapour phase epitaxy (MOVPE). The narrow X‐ray diffraction (XRD) peaks and clear Pendellosung fringes indicate that the GaAsN/GaAs interface is fairly flat and the GaAsN layers are uniform. By the photoluminescence (PL) measurement at 10 K, the clear PL peaks related to the near‐band‐edge transition could be detected and the bandgap energy was red‐shifted to 1.16 eV in 1.9%‐N GaAsN film. But, in higher N‐content films no peak could be detected. So, post growth annealing in the reactor was applied to 4.7% and 5.1%‐N films, and resulted in an enhancement of the PL peak intensity, and the bandgap energy of 5.1%‐N film was consequently determined to be 0.95 eV at room temperature. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Analysis of TMGa/NH3/H2reaction system in GaN-MOVPE growth by computational simulation

We report the major growth pathways of GaN metalorganic vapor-phase epitaxial growth from a TMGa/NH 3 /H 2 system studied by computational simulation. It has been found that the most major growth pathway is stepwise elimination of CH 4 from TMGa:NH 3 adducts (TMGa:NH 3 → DMGaNH 2 → MMGaNH → Ga-N → Growth), and the second major growth pathway is due to GaNH 2 molecules sublimated from GaN layer. [Ga-N] n was generated by polymerization of Ga-N molecules around the susceptor heated. GaN layer was deposited on not only the substrate but also the heated reactor walls.

Thermodynamic Aspects of Growth of AlGaN by High-Temperature Metal Organic Vapor Phase Epitaxy

The metalorganic vapor phase epitaxial (MOVPE) growth of AlGaN on AlN-coated sapphire at a temperature higher than 1,200 °C was carried out. Compared with that at a low-temperature growth regime in which alloy composition is determined by the flow rates of metalorganic Ga and Al sources, the solid composition of AlGaN is found to be strongly affected by thermodynamics.

Nitrogen content of GaAsN quantum wells by in situ monitoring during MOVPE growth

Metal–organic vapor phase epitaxial growth of GaAsN quantum wells is monitored by in situ reflectance measurements. Correlation between the change in the reflectance intensity and nitrogen content of the quantum well is established. The reflectance as a function of time also reveals if there is deterioration of the crystalline quality during growth. This method together with X-ray diffraction and photoluminescence characterization is applied to analyze GaAsN growth using various reactor pressures and TBAs/III molar flow ratios.

Oligomerization process in MOVPE growth of ZnO

AbstractChemical reactions in the vapor phase during metalorganic vapor phase epitaxy growth of ZnO are investigated with in‐situ monitoring using Fourier transform infrared spectroscopy. Diethylzin (DEZn) and nitrous oxide (N2O) were used for zinc and oxygen source, respectively. DEZn reacts first with oxygen atom generated from N2O dissociation, and changes to diethoxy zinc (DEOZn; Zn(OC2H5)2). Then C2H4 is eliminated from DEOZn at high temperature, and DEOZn changes to zinc dihydroxide (Zn(OH)2). In addition to these reactions, oligomerization of the reactants occurs, that is, they make their dimers, trimers, tetramers and higher‐order oligomers, and they contribute to the formation of ZnO on the substrates. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Dislocation reduction in GaN grown on porous TiN networks by metal-organic vapor-phase epitaxy

We report on the effectiveness of porous TiN nanonetworks on the reduction of threading dislocations (TDs) in GaN grown by metal-organic vapor-phase epitaxy (MOVPE). The porous TiN networks were formed by in situ annealing of thin-deposited Ti films deposited ex situ on GaN templates within the MOVPE growth chamber. Different annealing parameters in relation to surface porosity of TiN networks were investigated. Transmission electron micrographs indicated dislocation reduction by factors of up to 10 in GaN layers grown on the TiN nanonetwork, compared with a control sample. TiN prevented many dislocations present in the GaN templates from penetrating into the upper layer. Microscale epitaxial lateral overgrowth of GaN above TiN also contributed to TD reduction. The surface porosity of the TiN network had a strong impact on the efficiency of TD reduction. X-ray-diffraction and time-resolved photoluminescence measurements further confirmed the improved GaN quality.

MOVPE growth of Al-free 808 nm high power lasers using TBP and TBA in pure N 2 ambient

In metalorganic vapor-phase epitaxy (MOVPE) growth of III–V semiconductor compounds and device structures, arsine (AsH 3) and phosphine (PH 3) are normally used as group V precursors and hydrogen is used as the carrier gas, which is very toxic and has safety hazard. In this contribution, MOVPE growths of Al-free 808 nm high power diode lasers by using metalorganic (MO) group V sources, TBAs and TBP, and nitrogen as carrier gas has been reported. InGaAsP/InGaP/GaAs single quantum well (SQW) high power laser structure emitting at 808 nm has been adopted to characterize the material quality. Broad area stripe lasers with the stripe width of 150 μm have been fabricated from the wafers grown by the MOVPE using MO group V sources. Lasing of the device with threshold current density of 506 A/cm 2 has been successfully achieved.

Role of surface diffusion during selective area MOVPE growth of InP

Selective Area Metalorganic Vapor Phase Epitaxy (SA-MOVPE) growth of compound semiconductor, such as In 1– x Ga x As y P 1– y , is an indispensable technology to realize one-step fabrication of monolithic optical integrated circuits (OEICs). In SA-MOVPE, the growth rate of unmasked region is enhanced, because un-reacted group III precursors on the mask region diffuse into the epitaxial growth region. This growth rate enhancement is mainly caused by the gas-phase diffusion of precursors, but the contribution of surface diffusion becomes larger as the unmasked stripe becomes narrower. Moreover, in the SA-MOVPE growth of InP, the abnormal growth near the mask edge and the formation of tear-drop-like hillocks, which is considered to be originated from surface diffusion, are observed. In this work, the role of surface diffusion during SA-MOVPE growth of InP was investigated by measuring the cross-sectional area of abnormal growth and surface roughness. By changing the growth temperature from 793 K to 883 K, the area of abnormal growth increased and took maxima at 823 K, and decreased again at higher temperature. The concentration of group III precursor enhanced the abnormal growth and the roughness. The concentration effect was larger than the first order, and its relation to the surface diffusion length was suggested. This information on surface diffusion during SA-MOVPE is a key factor for the precise control of SA-MOVPE growth.

Highly reflective AlGaAsSb/InP Bragg reflector at 1.55 μm grown by MOVPE

The metalorganic vapor-phase epitaxy growth of a highly reflective 24-pair AlGaAsSb/InP-distributed Bragg reflector (DBR) is reported for the first time. The influence of the growth parameters such as the V/III input ratio, the growth temperature and the pressure, the total H 2 flow, the gas velocity and the switching sequence of the source gases at the interfaces has been deeply investigated and optimized to achieve stable growth conditions. The DBR achieves a reflectivity as high as 99.5% around 1.55 μm, a uniform stable composition, and an excellent crystal quality over the 2 inch wafer, with a surface free of crosshatch and a defect density below 1/cm 2. For the optical characterizations, measurements of linear and nonlinear reflectivity, transmission, pump-probe and photoluminescence were done. The interfaces and bulk layers of InP/AlGaAsSb/InP heterostructures were analyzed by transmission electron microscopy. High resolution X-ray diffraction measurements were used to determine the composition shift in the growth plane of the DBR. The measurements show the high quality of the growth and demonstrate that thick AlGaAsSb/InP heterostructures can be grown by metalorganic vapor-phase epitaxy (MOVPE), and in particular DBRs above 1.31 μm.

Preface: phys. stat. sol. (b) 242/13

AbstractWolfgang Richter celebrated his 65th birthday on 2 January 2005. On such an occasion, usually marking retirement, achievements and breakthroughs in research are reviewed. But Wolfgang Richter is not retiring: he has accepted an offer of a professorship at the University Rome II “Tor Vergata”. As he explained to us with his famous smile, he plans to concentrate his future efforts even more on his true love in science – the optical diagnostics of interfaces.Wolfgang Richter has been working in the field of optical spectroscopy of solids since his PhD studies at the University of Cologne. Having finished his PhD in 1969 in the field of infrared spectroscopy he decided to reduce the probed volume by increasing the energy of probing photons: Raman spectroscopy! During his postdoctoral and Habilitation periods (1970–1979) at Pennsylvania State University, Max‐Planck‐Institut für Festkörperforschung, and RWTH Aachen, he pursued his interest in resonance Raman spectroscopy on semiconductors.In 1979 he received his first appointment as full professor at the University of Ulm. He returned to RWTH Aachen in 1981 and discovered his true destiny: semiconductor interfaces. At that time in the Department of Semiconductor Technology, metal‐organic vapour phase epitaxy (MOVPE) was under development as a new technique for growing semiconductor layers. The underlying processes in MOVPE were known to be complex and very difficult to analyse with available experimental techniques, due to the unfriendly, reactive gas phase environment. Optical diagnostics turned out to be the key to a better understanding of MOVPE processes. Wolfgang Richter moved from RWTH Aachen to TU Berlin at the end of 1988 and began building a strong research group concentrating on interface analysis from two complementary sides: on the one hand, tracking MOVPE growth processes online by in situ optics and, on the other hand, advancing the fundamental understanding of optical spectra of interfaces by relating the optical response to atomic structures. Combining both aspects has finally led to considerable progress in surface and interface optics, as well as in vapour phase epitaxy and, moreover, the in situ optical tools developed are nowadays available as standard options in commercial MOVPE machines.The advances largely concerned the development of reflectance anisotropy spectroscopy and spectroscopic ellipsometry as in situ optical tools. However, considerable progress in Raman spectroscopy was also made: analysis of surfaces, ultrathin layers down to a single monolayer or even sub‐monolayer coverages, and sub‐wavelength spatial resolution were demonstrated in recent years. Current challenges concern, in particular, organic materials, molecule–solid interfaces and bio‐interfaces, which will help in the development of many new applications and devices. Interfaces will play a crucial role in many of these developments and optical spectroscopy offers promising capabilities for analysing such interfaces. Wolfgang Richter and his group at University of Rome II “Tor Vergata” are sure to be active in this emerging field for a long time to come.Based on a symposium on Optical Spectroscopy of Interfaces at the Spring Meeting of the German Physical Society in Berlin 2005, we have asked former and present colleagues of Wolfgang Richter to contribute to this special issue of physica status solidi (b) on “Advanced Optical Diagnostics of Surfaces, Nanostructures and Ultrathin Films”. We think that the collection of 26 papers gives an excellent overview on recent achievements and future developments in the field of linear optics. In addition to a number of Original Papers on experimental work and some Review Articles, the issue includes examples of the current approaches of computational theory to solid state optics and interface optics. We hope that this issue will stimulate the expansion of the growing field of optical analysis of interfaces, nanostructures and ultrathin layers into new areas of basic and applied science. After the success in characterising inorganic materials, it is surely time that the potential of optical spectroscopy techniques for probing thin films and interfaces of composite (organic–inorganic) materials was considered.5 October 2005

Development and control of MOVPE growth processes for devices using reflectance anisotropy spectroscopy and normalized reflectance

AbstractThe use of the optical in situ techniques reflectance anisotropy (RA) and normalized reflectance (NR) for metal‐organic vapour‐phase epitaxy (MOVPE) growth processes of compound semiconductor devices is reviewed. The RA signal detects small deviations in the doping profile during growth of hetero‐bipolar transistors and correlates to the emission wavelength of edge‐emitting laser structure via its sensitivity to the quantum well composition. The NR signal is crucial for the alignment of distributed Bragg reflectors (DBR) in vertical‐cavity surface‐emitting lasers. With simultaneously performed RA and NR measurements the doping profile as well as the DBR alignment can be determined in situ. The composition monitoring in quaternary InGaAsP grown on InP is demonstrated using the RA signal for the As:P ratio while the NR signal is used for the Ga:In ratio. For AlGaInP on GaAs the NR signal is sensitive to both the aluminium and the indium content. Therefore these effects have to be separated via the determination of the growth efficiency of the respective materials using the growth rate calculated from the NR signal. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Low-temperature MOVPE growth of ZnO thin films by using a buffer layer

ZnO thin films have been grown on a-plane (1,1,−2,0) sapphire substrates by metalorganic vapor phase epitaxy (MOVPE) at low substrate temperature of 350 °C. It is showed that the crystal and electrical quality of the thin films was improved by using a ZnO buffer layer. The photoluminescence (PL) measurements indicate that the ZnO thin films grown at such a low substrate temperature have a strong UV emission.

Highly strained InGaAs∕GaAs multiple quantum-wells for laser applications in the 1200–1300 nm wavelength regime

We report on metalorganic vapor-phase epitaxy growth optimization and properties of highly strained InGaAs∕GaAs quantum-well (QW) structures with emission wavelength beyond 1200 nm. It is observed that a sufficiently high V/III ratio in combination with low growth temperature is critical for preserved layer integrity when increasing the strain. Multiple QWs with up to five wells are realized without any degradation in photoluminescence intensity or broad-area laser performance at an emission wavelength of 1240 nm with threshold current density below 70A∕cm2 per well.

Catalyst-free growth of GaAs nanowires by selective-area metalorganic vapor-phase epitaxy

We report on the fabrication of GaAs hexagonal nanowires surrounded by {110} vertical facets on a GaAs (111) B substrate using selective-area (SA) metalorganic vapor-phase epitaxial (MOVPE) growth. The substrate for SA growth was partially covered with thin SiO2, and a circular mask opening with a diameter d0 of 50–200 nm was defined. After SA-MOVPE, GaAs nanowires with a typical diameter d ranging from 50 to 200 nm and a height from 2 to 9μm were formed vertically on the substrate without any catalysts. The size of the nanowire depends on the growth conditions and the opening size of the masked substrate. A possible growth mechanism is also discussed.

Fabrication of ultrathin and highly flexible InP-based membranes for microoptoelectromechanical systems at 1.55 /spl mu/m

Tunable microcavities have been fabricated to evaluate their tunability in dependence on the membrane thickness. The membrane thickness has been decreased from 615 nm down to a record thickness of 123 nm yielding in a maximum mechanical tunability of 15.15 nm/V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Furthermore, a three-period /spl lambda//4 InP/air-gap high reflective mirror (R > 99.8% at 1.55 μm) with a record wide stopband of more than 1100 nm has been fabricated. These results are achieved thanks to specific metal-organic vapor-phase epitaxy growth parameters.