Selective-area Metalorganic Vapor Phase Epitaxy Research Articles

Selective-area MOVPE fabrication of GaAs hexagonal air-hole arrays on GaAs(111)Bsubstrates using flow-rate modulation mode

GaAs hexagonal air-hole arrays fabricated by selective-area metal-organic vapour phaseepitaxy (SA-MOVPE) on patterned GaAs(111)B substrates are promising for applicationsto hexagonal air-hole-type two-dimensional photonic crystal (2D-PhC) slabs,because the grown structures exhibit smooth flat surfaces surrounded by crystalfacets. In this paper, we describe SA-MOVPE carried out under various gas-flowsequences in order to reduce the growth temperature, and to obtain uniform air-holearrays without lateral over-growth (LOG). We found that the growth rate in thepattern region and LOG were closely related to the effective As coverage and thedesorption rate of the source materials. By optimizing SA-MOVPE, we obtaineduniform hexagonal air-hole arrays with almost no LOG for arrays with 500–400 nmperiodicity using alternate supply of the source materials (flow-rate modulationepitaxy mode). Finally, we successfully fabricated air-bridge-type hole arrays usingselective etching of a sacrificial layer for vertical confinement of light in 2D-PhCs.

Fabrication and characterization of freestanding GaAs∕AlGaAs core-shell nanowires and AlGaAs nanotubes by using selective-area metalorganic vapor phase epitaxy

We fabricated GaAs∕AlGaAs core-shell nanowires by using selective-area metalorganic vapor phase epitaxy. First, GaAs nanowires were selectively grown on partially masked GaAs (111)B substrates; then AlGaAs was grown to form freestanding heterostructured nanowires. Investigation of nanowire diameter as a function of AlGaAs growth time suggested that the AlGaAs was grown on the sidewalls of the GaAs nanowires, forming GaAs∕AlGaAs core-shell structures. Microphotoluminescence measurements of GaAs and GaAs∕AlGaAs core-shell nanowires reveal an enhancement of photoluminescence intensity in GaAs∕AlGaAs core-shell structures. Based on these core-shell nanowires, AlGaAs nanotubes were formed by using anisotropic dry etching and wet chemical preferential etching to confirm the formation of a core-shell structure and to explore a new class of materials.

A 1 bit binary-decision-diagram adder circuit using single-electron transistors made by selective-area metalorganic vapor-phase epitaxy

We demonstrate single-electron operation of a 1 bit adder circuit using GaAs single-electron tunneling transistors (SETs). GaAs dot and wire coupled structures for the fabrication of SETs were grown by a selective-area metalorganic vapor-phase epitaxy technique. The logic circuit was realized based on a binary decision diagram architecture using Coulomb blockade (CB) in GaAs dots and switching operations were achieved in a single-electron mode because of the CB effects. Through this architecture, a 1 bit adder circuit was realized with three SETs, two of which were for AND logic and one with two input gates for exclusive OR (XOR). Both AND and XOR operations were demonstrated at 1.9 K, which indicated successful fabrication of the 1 bit adder.

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.

Promising low-damage fabrication method for the photonic crystals with hexagonal or triangular air holes: selective area metal organic vapor phase epitaxy

The photonic band diagrams of the photonic crystal slabs (PCSs) with various structural air holes were calculated by plane wave expansion method with super cell method. The calculated results indicate that the PCSs with hexagonal or triangular air holes have enough large photonic band gaps in the guided mode spectrum, hence they are good candidates to be used for the PC devices. The PCs with hexagonal or triangular air holes were fabricated successfully on n-type GaAs (111)B substrate by selective-area metal organic vapor phase epitaxy (SA-MOVPE). Vertical and smooth facets are formed and the uniformities are very good. The same process was also used to fabricate hexagonal air hole arrays with the width of 100 nm successfully. A procedure was proposed and utilized to fabricate the air-bridge PCS with normal hexagonal air holes. The fabricated hexagonal air holes are very uniform and the sidewalls are smooth and vertical. Our experimental results indicate that SA-MOVPE growth is a promising low-damage fabrication method for PC devices and photonic nano-strucutres.

Fabrication and characterization of GaAs two-dimensional air-hole arrays on GaAs (1 1 1)A substrates using selective-area MOVPE

We report on the selective-area metal-organic vapor-phase epitaxial (SA-MOVPE) growth of GaAs-based periodic air-hole arrays on partially masked GaAs (1 1 1)A substrates for application to two-dimensional photonic crystals (2D PhCs). We obtained uniform 1-μm-pitch GaAs 2D air-hole arrays on GaAs (1 1 1)A substrates with vertical side walls under high AsH 3 partial pressure and low-growth-rate conditions. However, under these growth conditions, lateral over-growth (LOG) occurs at three corners of hexagonal air-hole, and the hole shape change to triangle. We clarified the mechanism of selective area growth on a GaAs (1 1 1)A substrates. We also tried shorter pitch (400 nm) GaAs air-hole arrays and AlGaAs SA-MOVPE on GaAs (1 1 1)A.

MOVPE selectively grown GaAs nano-wires with self-aligned W side gate

We have fabricated GaAs/AlGaAs nano-wire field effect transistors (FETs) having novel self-aligned tungsten ( W) gate electrode by using selective-area metal organic vapor-phase epitaxy (SA-MOVPE). Stacked film of SiO 2/W was used as a mask for SA-MOVPE, where W is to form self-aligned gate on the side of the nano-wire structure, while SiO 2 deposited on W is used to prevent lateral growth over the mask. With an appropriate design for the wire width, W, the distance, H, between the channel and the gate, FET action with good pinch-off and transfer characteristics was demonstrated at room temperature. Maximum transconductance g m of 600 μ S / μ m was achieved with a nanowire FET with channel width ( W = 80 nm ).

Fabrication of GaAs nanowire devices with self-aligning W-gate electrodes using selective-area MOVPE

We propose and demonstrate a novel self-aligning process for fabricating the tungsten (W) gate electrode of GaAs nanowire FETs by using selective-area metalorganic vapor phase epitaxy (SA-MOVPE) where SiO 2/W composite films are used to mask the substrates. First, to study the growth process and its dependence on mask materials, GaAs wire structures were grown on masked substrates partially covered with a single W layer or SiO 2/W composite films. We found that lateral growth over the masked regions could be suppressed when a wire along the [110] direction and a SiO 2/W composite mask were used. Using this composite mask, we fabricated GaAs narrow channel FETs using W as a Schottky gate electrode, and we were able to observe FET characteristics at room temperature.

Growth of GaAs/AlGaAs hexagonal pillars on GaAs (1 1 1)B surfaces by selective-area MOVPE

We report on the growth of GaAs and GaAs/AlGaAs heterostructured hexagonal pillar structures using selective area (SA) metalorganic vapor phase epitaxy (MOVPE). By performing growth on SiO 2-masked (1 1 1)B GaAs substrates with circular or hexagonal hole openings, extremely uniform array of hexagonal GaAs/AlGaAs pillars consisting {1 1 0} vertical facets with their diameter of order of 100 nm were obtained. Unexpectedly, strong intense light emission was observed for the room temperature photoluminescence measurement of the pillar arrays in triangular lattice, which is promising for the application to the photonic crystals to enhance the light extraction efficiency from the materials with high refractive index. Furthermore, it was also found that hexagonal pillars with size 60 nm and large aspect ratio (>100) by reducing the size of initial hole size of mask, opening a possibility to grow nanowires using epitaxial growth.

Growth of GaAs/AlGaAs hexagonal pillars on GaAs (111)B surfaces by selective-area MOVPE

We report on the growth of GaAs and GaAs/AlGaAs heterostructured hexagonal pillar structures using selective area (SA) metalorganic vapor phase epitaxy (MOVPE). By performing growth on SiO2-masked (1 1 1)B GaAs substrates with circular or hexagonal hole openings, extremely uniform array of hexagonal GaAs/AlGaAs pillars consisting {110} vertical facets with their diameter of order of 100nm were obtained. Unexpectedly, strong intense light emission was observed for the room temperature photoluminescence measurement of the pillar arrays in triangular lattice, which is promising for the application to the photonic crystals to enhance the light extraction efficiency from the materials with high refractive index. Furthermore, it was also found that hexagonal pillars with size 60nm and large aspect ratio (>100) by reducing the size of initial hole size of mask, opening a possibility to grow nanowires using epitaxial growth.

Realization of InAs-based two-dimensional artificial lattice by selective area metalorganic vapor-phase epitaxy

The experimental realization of two-dimensional semiconductor artificial lattice based on InAs quantum wires is reported here. Artificial Kagome lattice fabricated using InAs quantum wires of unit cell size 0.7 μm has been theoretically proved to show ferromagnetism. Fabrication of such a structure with InAs quantum wires was attempted by selective area metalorganic vapor phase epitaxy using GaAs (111)A substrates. Temperature-dependent growth mode change was observed and Volmer-Weber growth mode at high temperature inhibited the formation of uniform structure. Low temperature and low AsH3 partial pressure resulted in the successful fabrication of 0.7 μm period InAs-based Kagome lattice structure.

Photocurrent spectroscopy of a (0 0 0 1)GaN/AlGaN/(1 1 1)Si heterostructure

A crack-free GaN/AlGaN sample was grown on (1 1 1) Si by selective area metal-organic vapor-phase epitaxy method using an AlGaN intermediate layer. The electrical properties of the GaN/AlGaN/Si heterojunction diode were investigated with photocurrent spectroscopy at 77 K . It was found that the current–voltage characteristics depend on the thickness/composition of the intermediate layer. The photocurrent spectra indicated that the energy band of the n-type-doped Si substrate is lifted at the heterointerface, while it is flat in case of the sample grown on a p-type-doped Si. The depletion of the energy band in the n-Si at the heterointerface is attributed to the diffusion of Al during the growth.

Selective area MOVPE growth of InP and InGaAs pillar structures for InP-based two-dimensional photonic crystals

Fabrication of high-quality photonic crystals (PCs) is an important issue for precise control of photon propagation. In particular, high aspect ratio, smooth surface, and high uniformity are required to achieve two-dimensional PCs (2DPCs). We report on the fabrication of InP and InGaAs pillar structures on InP substrates by using selective area metal-organic vapor-phase epitaxy (SA-MOVPE) for application to InP-based 2DPCs. This method is very promising as a way to form semiconductor 2DPCs because it makes it possible to obtain PC structures without process-induced damage. To form uniform pillar arrays, we investigated the properties of SA-MOVPE growth on InP (1 1 1) A and (1 1 1) B substrates. We found that pillar shapes strongly depended on the TBP pressure and growth temperature, and on the optimum growth conditions of uniform pillar structures having {1 1 0} vertical side facets.

Polycrystals growth on dielectric masks during InP/GaAs selective MOVPE

In selective-area metalorganic vapor-phase epitaxy, polycrystals are generated on masks of large area. The generation of such crystals should be avoided because they act as uncontrollable sink of film precursors. Although generation of polycrystals is sometimes associated with surface migration of a precursor on masks, our observation suggested that polycrystals are generated when the gas-phase concentration of a film precursor just above masks exceeds a critical value. Reducing either total pressure or partial pressure of the source gas suppressed generation of polycrystals, which is consistent with the gas-phase mechanism. The threshold of gas-phase precursor concentration for generation of polycrystals was investigated as a function of growth temperature and V/III ratio for both GaAs and InP. The threshold increased with temperature, that is to say, fewer polycrystals were observed at higher temperature. The threshold for InP was significantly larger than that for GaAs. This information is useful for designing mask patterns which do not generate polycrystals, and it helps to provide a detailed understanding of nucleation phenomena.

Single-electron AND/NAND logic circuits based on a self-organized dot network

We experimentally demonstrated single-electron operations of an AND/NAND logic circuit based on a self-organized GaAs quantum-dot (QD) network fabricated by applying a selective-area metalorganic vapor-phase epitaxy technique. Single-electron logic operations using four cooperating single-electron tunneling (SET) transistors has been tested. This logic circuit has an architecture based on a binary decision diagram (BDD) using a Coulomb blockade (CB) in GaAs QDs, which is a representation of digital logic functions using directed graphs. BDD node devices consisting of two SET transistors achieved a two-way path switching operation in single-electron mode due to the CB effects which appeared complementarily in the two SET transistors at 1.9 K. We also demonstrated an AND/NAND operation in a logic circuit by integrating two BDD nodes.

Formation and characteristics of 100-nm scale GaAs quantum wires by selective area MOVPE

We fabricated quantum wires (QWRs) with sub-micron wire width using GaAs/AlGaAs selectively doped structures grown by selective area metalorganic vapor phase epitaxy (SA-MOVPE) on (0 0 1) masked GaAs substrates partially covered by SiON. From the measurement of a two-terminal conductance as a function of geometrical wire width, QWRs with effective channel width <100 nm are formed without application of any gate bias. The magnetoresistance measurement at 1.7 K also suggests the formation of narrow QWRs, although it also indicates a presence of potential fluctuation along the QWRs. The effective channel width of present QWRs are much narrower than the previously reported values (∼300 nm) of those formed by SA-MOVPE.

Growth and Optical Properties of 2D Photonic Crystals Based on Hexagonal GaAs/AlGaAs Pillar Arrays by Selective-Area Metalorganic Vapor Phase Epitaxy

ABSTRACTWe report on the growth of GaAs and GaAs/AlGaAs heterostructured hexagonal pillar arrays using selective area (SA) metalorganic vapor phase epitaxy (MOVPE) for the application of two-dimensional photonic crystals (2D-PhCs). SA-MOVPE was carried out on SiO2 masked (111)B GaAs substrates with circular or hexagonal hole openings. Extremely uniform array of hexagonal GaAs/AlGaAs pillars consisting {110} vertical facets with their diameter of order of 200 nm were obtained. Unexpectingly strong intense light emission was observed for the room temperature photoluminescence measurement, which suggests low surface nonradiative recombination and enhancement of the light extraction efficiency of the pillar arrays.

Formation of nanoscale heterointerfaces by selective area metalorganic vapor-phase epitaxy and their applications

We describe fabrication methods of GaAs and InAs quantum dot (QD) structures and related semiconductor nanostructures having nanoscale heterointerfaces grown by the selective area metalorganic vapor-phase epitaxial (SA-MOVPE) method on partially masked GaAs substrates. GaAs QD arrays and wire–dot coupled structures having strong lateral confinement were fabricated on appropriately designed masked substrates. InAs QDs were also formed on various kinds of GaAs pyramidal and wire structures, where site-selective formation is demonstrated by the combination of self-assembling growth mode and selective area growth. The application of QDs to single-electron transistors using SA-MOVPE is also described.

Formation of InAs Dots on AlGaAs Ridge Wire Structures by Selective Area MOVPE Growth

We investigate the formation of InAs quantum dots (QDs) on the top of AlGaAs ridge wire structures along the [110] direction by selective-area metalorganic vapor phase epitaxy (SA-MOVPE) and study their size distribution. It is found that the size distribution of QDs depends on the top width W of AlGaAs wires and growth amount θ of InAs. InAs dot size across the AlGaAs wires are limited by W and it becomes uniform for narrower W. In contrast, the size along the wire exhibits non-uniformity, particularly for narrower W and large θ. In addition, the shapes of InAs dot change depending on W. The results are discussed based on the diffusion of In from facets and masked area and the coalescence of QDs.

Selective area MOVPE growth of two-dimensional photonic crystals having an air-hole array and its application to air-bridge-type structures

We describe a novel fabrication method of two-dimensional photonic crystals (2DPCs) by using selective area metal-organic vapor-phase epitaxial (SA-MOVPE) growth on (1 1 1) B masked substrates and its application to air-bridge-type structures with selective wet-chemical etching. This method is very promising as a way to form semiconductor 2DPCs because a PC membrane without process-induced damages can be obtained. To form uniform PC membranes having an air-hole array, we investigated the properties of SA-MOVPE regrowth on sub-micron-pitch masked substrates. We found that the optimum growth conditions strongly depend on the width of the GaAs opening as well as the pitch of the 2DPCs. An air-bridge structure having 250-nm-pitch 2DPC was also demonstrated by using a combination of SA-MOVPE regrowth and selective wet-chemical undercut etching.