Aluminum Nitride Single Crystals Research Articles

Preparation and Characterization of Single-crystal Aluminum Nitride Substrates

Large (up to 10mm diameter) aluminum nitride (AlN) boules have been grown by the sublimation-recondensation method to study the preparation of high-quality single crystal substrates. The growth mechanism of the boules has been studied using AFM. It has been determined that large single crystal grains in those boules grow with a density of screw dislocations below 5×104 cm−3 while edge dislocations are at lower density (none were observed). High-quality AlN single crystal substrates for epitaxial growth have been prepared and characterized using Chemical Mechanical Polishing (CMP) and AFM imaging, respectively. Also, the differential etching effect of KOH solutions on the N and Al-terminated faces of AlN on vicinal c-faces has been investigated. In order to identify the N or Al-terminated face, convergent beam electron diffraction has been used.

Preparation and Characterization of Single-crystal Aluminum Nitride Substrates

AbstractLarge (up to 10mm diameter) aluminum nitride (AlN) boules have been grown by the sublimation-recondensation method to study the preparation of high-quality single crystal substrates. The growth mechanism of the boules has been studied using AFM. It has been determined that large single crystal grains in those boules grow with a density of screw dislocations below 5×104 cm−3 while edge dislocations are at lower density (none were observed). High-quality AlN single crystal substrates for epitaxial growth have been prepared and characterized using Chemical Mechanical Polishing (CMP) and AFM imaging, respectively. Also, the differential etching effect of KOH solutions on the N and Al-terminated faces of AlN on vicinal c-faces has been investigated. In order to identify the N or Al-terminated face, convergent beam electron diffraction has been used.

Sublimation growth and characterization of bulk aluminum nitride single crystals

Single crystalline platelets of aluminum nitride (AlN) ⩽ 1 mm thick have been grown within the temperature range of 1950–2250°C on 10 × 10 mm2 α(6H)-silicon carbide (SiC) substrates via sublimation-recondensation in a resistively heated graphite furnace. The source material was sintered AlN. A maximum growth rate of 500 μm/h was achieved at 2150°C and a source-to-seed separation of 4 mm. Growth rates below 2000°C were approximately one order of magnitude lower. Crystals grown at high temperatures ranged in color from blue to green due to the incorporation of Si and C from the SiC substrates; those grown at lower temperatures were colorless and transparent. Secondary-ion mass spectroscopy (SIMS) results showed almost a two order of magnitude decrease in the concentrations of these two impurities in the transparent crystals. Plan view transmission electron microscopy (TEM) of these crystals showed no line or planar defects. Raman spectroscopy and X-ray diffraction (XRD) studies indicated a strain free material.

Preparation of aluminum nitride thin films by reactive sputtering and their applications to GHz-band surface acoustic wave devices

Single crystal aluminum nitride (AlN) thin films were prepared by a low-temperature reactive sputtering on basal plane sapphire [(001)Al2O3] at a substrate temperature of less than 315 °C. Surface acoustic wave (SAW) characteristics with an interdigital transducer /(001)AlN/(001)Al2O3 structure were investigated. The phase velocity and temperature coefficient of delay time are 5750–5765 m/s and 55–63 ppm/°C at KH=1.2–1.6, respectively. Resonator-type 1-GHz-band SAW filters with its structure were fabricated. The insertion loss and suppression were 23 dB and more than 20 dB, respectively.

Raman-scattering studies of aluminum nitride at high pressure.

Single crystals of aluminum nitride were studied by Raman scattering under hydrostatic pressure up to 13 GPa. Four of the six allowed modes were observed and identified. Our results under ambient conditions do not agree with already published data. The ${\mathit{A}}_{1}$(TO), ${\mathit{E}}_{2}^{(2)}$, and ${\mathit{E}}_{1}$(LO) have been followed as a function of pressure and have mode-Gr\"uneisen coefficients of 1.58, 1.26, and 0.38, respectively. These data are compared with recent data obtained on single crystals of gallium nitride.

On the nature of the oxygen-related defect in aluminum nitride

The oxygen-related defect in an aluminum nitride (AIN) single crystal and in polycrystalline ceramics is investigated utilizing photoluminescence spectroscopy, thermal conductivity measurements, x-ray diffraction lattice parameter measurements, and transmission electron microscopy. The results of these measurements indicate that at oxygen concentrations near 0.75 at.%, a transition in the oxygen accommodating defect occurs. On both sides of this transition, simple structural models for the oxygen defect are proposed and shown to be in good agreement with the thermal conductivity and lattice parameter measurements, and to be consistent with the formation of various extended defects (e.g., inversion domain boundaries) at higher oxygen concentrations.

Epitaxial Growth of Aluminum Nitride on Sapphire Using Metalorganic Chemical Vapor Deposition

Epitaxial aluminum nitride (AlN) films were grown on the basal planes of sapphire substrates using metalorganic chemical vapor deposition (MO-CVD), and the following results were obtained. (1) The substrate temperature and the trimethylaluminum (TMA) concentration dependences of the growth rate suggested that the growth process is limited by mass transport. (2) The crystalline perfection of epitaxial films is strongly affected not only by the substrate temperature but also by the gas flow pattern. (3) Single-crystal AlN films which include no misoriented grains can be grown epitaxially at ∼1200°C under carefully-controlled gas flow patterns. (4) Crystalline imperfection is caused mainly by (1 1̄01)-oriented grains which correspond to the hillocks observed in the surface morphology.

Aluminum nitride films by rf reactive ion-plating

Aluminum nitride films were synthesized successfully on silicon (111) and spinel (111) single crystal surfaces by rf reactive ion-plating. Aluminum was evaporated from an evaporator in the rf discharge phase of either nitrogen gas or ammonia gas at a pressure of 10−4 Torr (∠10−2 Pa). Film structures were evaluated using reflection high energy electron diffraction (RHEED) and scanning electron microscopy (SEM). The aluminum nitride films synthesized on the spinel (111) surfaces at the substrate temperature of 1000 °C, in the rf discharge phase of both nitrogen gas and ammonia gas, were found to be of single crystal form, having parallel orientation to the substrate surfaces. Aluminum nitride single crystals forming hexagonal pyramids were observed to grow in the perpendicular direction to the substrate surfaces during the study. The growth rate of aluminum nitride film obtained in the ammonia gas discharge, which was about 500 Å min−1, was about two times as fast as that obtained in the nitrogen gas discharge.

Ain single crystals

Single crystals of aluminum nitride up to 1 cm long and 0.3 in diameter have been grown by a sublimation-recondensation technique at about 2250°C. The starting material is prepared by the direct reaction of aluminum and nitrogen at 1850°C. The crystals are grown at a rate of 0.03 cm/hr. in sealed tungsten crucibes in an rf heated tungsten furnace. They are amber in color and have the wurtzite structure.

Growth of single crystals of aluminum nitride

The growth mechanism and the growth condition of single crystals of aluminum nitride (AlN) prepared by the sublimation method are studied in relation with their morphology. The whiskers of AlN, whose growth directions are perpendicular to the (10-10) plane (a-type whiskers), the (10-11) plane (b-type whiskers) and the (0001) plane (c-type whiskers) grow through the VLS mechanism, iron acting as liquid-forming agent in the mechanism. The growth directions of whiskers depend on the growth temperature; the c-type whiskers grow above 1550°C, the a-type above 1700°C and the b-type above 1850°C. Blade-shaped crystals with large (0001) faces (a-type crystals) grow from lateral surfaces of the a-type whiskers.Prismatic crystals with large prismatic (10-10) faces (P-type crystals) and tabular crystals with large (0001) faces (T-type crystals) grow above 1900°C in the atmosphere free from iron. The P-type crystals grow in the circumstance of high purity. The T-type crystals grow in the atmosphere comprising carbon mono-oxide.Growth spirals are observed on the (0001) face of the T-type crystals. The growth steps parallel to the c-axis and a-axis observed on the (10-10) face of the P-type crystals.

The synthesis of aluminum nitride single crystals

Small bipyramidal (1.1 mm long × 0.3 mm wide), good optical quality aluminum nitride single crystals have been reproducibly grown from molten AlNCa 3N 2 solutions.

VLS機構による窒化アルミニウム単結晶の成長

VLS機構による窒化アルミニウム単結晶の成長

Epitaxial growth of aluminum nitride

The epitaxial growth of aluminum nitride on the basal planes of hexagonal silicon carbide and aluminum nitride substrates has been studied using the ammonolysis of aluminum trichloride in a gas flow system. Adherent and continuous films were obtained under a wide range of experimental conditions, and the substrate temperature is the most influential factor determining the crystalline perfection of the deposit. In the temperature range 1200–1250°C, single crystal aluminum nitride films epitaxial with respect to the substrates, as thick as 25 μ, have been deposited reproducibly by using reactant mixtures with AlCl 3/NH 3 molar ratios in the range of 5 × 10 −4 to 5 × 10 −3. The use of mercury and hydrogen selenide as dopants has produced, respectively, p- and n-type aluminum nitride films.

Space charge conduction and electrical behaviour of aluminium nitride single crystals

Hall mobility, optical absorption and thermal activation energy have been measured on single crystals of aluminium nitride grown from the vapour phase. Colourless crystals have a resistivity of about 10 12 ohm cm and behave in a strongly non-ohmic manner for large applied fields. Blue crystals have a resistivity of about 10 4 ohm cm and are p-type.