【Member News】SINOGa Valley's Patent on “Dynamic Atmosphere Control in Gallium Oxide VGF Growth” Published: From One Atmosphere per Furnace to Segmented Atmosphere Control

      In crystal growth furnaces, the hardest factor to control is often not temperature, but the invisible atmosphere inside the furnace. Recently, the China National Intellectual Property Administration (CNIPA) published a new patent application from SINOGa Valley, titled “Dynamic Atmosphere Control Method, Equipment, and Medium for VGF Growth of Gallium Oxide” (Publication No. CN122959851A). The patent addresses precisely this challenge.

01 Two Major Challenges in Gallium Oxide Crystal Growth

      Gallium oxide single crystals have a melting point of approximately 1,820°C. In high-temperature crystal growth, the real challenge lies in the fact that gallium oxide tends to decompose while melting.

Decomposition and Volatilization

      Gallium oxide begins to decompose well below its melting point. The primary volatile species include lower-valence gallium oxides such as Ga₂O and GaO, as well as metallic gallium. This causes the melt composition to deviate from its intended stoichiometry, while metallic gallium gradually accumulates. As a result, oxygen vacancies become more abundant in the grown crystal.

Formation of Crystallographic Defects

      An asymmetric temperature field, thermal stress, seed crystal orientation, and fluctuations at the solid–liquid interface can easily induce defects such as twin boundaries, mosaic structures, screw dislocations, and crystal cleavage or cracking.

      VGF (Vertical Gradient Freeze) is a directional solidification method in which the crystal grows upward from the bottom of a crucible. The crystal and crucible remain stationary relative to each other, with neither pulling nor crucible movement involved. Its axial temperature gradient is also gentler than that of EFG. VGF offers greater flexibility in crucible selection, with both iridium and platinum-rhodium alloy crucibles being used. The latter offers oxidation resistance, allowing crystal growth in air or even under higher oxygen partial pressures.

      However, conventional VGF still has a limitation: as a single boule grows upward from the bottom, the melt surface, the advancing solid–liquid interface, and the already-solidified crystal each have different atmospheric requirements. As the interface moves upward, these requirements change accordingly. A uniform gas supply throughout the furnace can only meet the needs of one of these regions at a time.

02 Patent Analysis: Dividing Atmosphere Control into Three Zones

      To address the challenges outlined above, the newly published patent from SINOGa Valley proposes a refined dynamic atmosphere control scheme built around two key features:

      First, independent temperature and gas supply control across three zones. The vertical VGF single-crystal growth furnace is divided into three functional zones along the axial direction of the crucible. The zones are gas-isolated from one another, with independent temperature control and gas supply. A multi-parameter real-time monitoring system and centralized closed-loop control are also integrated, allowing monitoring data to feed directly into atmosphere regulation.

      Second, differentiated atmosphere management throughout the entire growth process:

Pre-Growth Stage

      The furnace chamber undergoes gas purging and preheating, while an initial axial oxygen partial pressure gradient that decreases from one zone to the next is established.

Crystal Growth Stage

      Based on real-time monitoring data, oxygen partial pressure is controlled independently in each zone. As the solid–liquid interface moves axially, the system simultaneously adjusts the coverage range and atmosphere parameters of each zone to accommodate the growth requirements of different sections of the boule.

Post-Growth Stage

      The atmosphere is switched to an inert gas environment with low oxygen partial pressure, followed by an annealing program involving a gradual, stepped reduction in temperature. Slow cooling helps release thermal stress within the crystal and reduce the risk of cracking. At the same time, it avoids the temperature range in which precious-metal crucibles are particularly susceptible to oxidation, thereby reducing crucible wear.

      From “one atmosphere throughout the furnace” to “segmented gas supply that follows the moving interface.”

      SINOGa Valley's primary focus is the industrial-scale delivery of (001) gallium oxide substrates with zero twin boundaries. The edge-defined film-fed growth (EFG) method is currently its main production technology, while VGF and dynamic atmosphere control serve as process technologies in reserve for large-size, low-defect crystal growth. These complementary approaches all serve the same goal: making substrate consistency reproducible and enabling predictable batch delivery.