TDI GaN, AlN and AlGaN Epitaxial Wafer Fab, Silver Spring, MD, USA

TDI is moving its entire manufacturing operations to a new 3,200m² facility in Silver Spring, Maryland. The new facility has expanded R&D and manufacturing space for crystal growth, epitaxial deposition and material characterization.

TDI's substrates are suitable for the fast growing blue/green/ultraviolet (UV) LED and laser diode market. The fab will initially be geared for the mass production of GaN, AlN and AlGaN epitaxial wafers. TDI has several novel template based processes including GaN on sapphire and AlN on SiC. Follow-on product lines at the new facility will include the company's True Bulk GaN.

SUBSTRATES FOR BLUE/GREEN/UV LEDs AND LASER DIODES

Blue High Brightness LEDs are exciting devices because of their potential benefits in the huge domestic and office lighting market. White light is generally produced from semiconductors by either covering blue LEDs with phosphors that glow white or using multiple red/green/blue LEDs in a single housing. HB-LEDs are now even bright enough to be used in outdoor (and indoor) displays.

Blue GaN lasers have short wavelengths to increase packing densities of CD/DVD and optical drives, and sharpness of laser printers. The business will receive another boost when next generation Blu-ray DVDs (Digital Versatile Disks) become available.

A major obstacle to widespread use of GaN is the cost, however, and TDI's site will be hosting a number of interesting processes that help solve the problem.

GaN ON SAPPHIRE SUBSTRATES

Blue LEDs are today generally grown on sapphire substrates which involves extensive sapphire substrate pretreatment (heating to 1,000°C to 1,100°C, cooling to 600°C to deposit GaN nucleation layer, reheating to 1,000°C to grow thick conducting GaN buffer layer).

TDI claims a proprietary process that eliminates all this pretreatment, growing multi-layer LEDs directly on the wafer surface. The substrate has a high quality 2 to 5 micron thick (silicon doped) n-type GaN epitaxial layer. Structures can include cladding layers, multiple quantum-wells and p-type layers.

The new facility is using a greatly simplified manufacturing process. The process improves yield by eliminating complex and sensitive growth steps, while homoepitaxial growth improves device characteristics. The process is a retrofit and TDI claims it reduces MOCVD growth time by more than 30% and increases throughput by 30% to 50% without capital expenditure. It also reduces the use of chemicals like TMG and ammonia.

The company can supply thousands of high quality GaN-on-sapphire templates per month using the technique.

GROUP III/V NITRIDES SEMI-INSULATING SUBSTRATES

TDI has recently developed semi-insulating substrate materials for nitride-based devices like GaN, AlN, InN and alloys. Devices have a 20 micron thick single crystal AlN film deposited on a silicon carbide (SiC) substrate. 2in diameter samples are available and TDI is ramping up production at the site for larger size wafers.

The substrates have good lattice and thermal match to GaN-based devices with high thermal conductivity SiC substrate and high electrical resistivity of AlN. They aim at applications like ultra high power AlGaN/GaN high electron mobility transistors (HEMTs), and blue/UV LEDs and laser diodes (LDs).

BULK GaN SUBSTRATES

Besides allowing rapid commercialization of GaN epi wafers, the new fab will allow TDI to speed up development of bulk GaN substrates. GaN is one of the few compound semiconductor materials not yet available as a commercial substrate. So, all currently available GaN-based devices are necessarily grown epitaxially on non-native substrates such as SiC or sapphire which are, by definition, lattice mismatches to GaN.

TDI's proprietary True Bulk GaN involves bulk GaN crystal growth, crystal slicing, polishing and final surface preparation.

GaN, AlN AND SiC SEMICONDUCTING MATERIALS

TDI was founded in Gaithersburg, Maryland in 1997. The company is a privately owned developer and manufacturer of compound semiconductor materials like GaN, AlN and SiC. In addition to bulk and epitaxial GaN projects, TDI is developing various compound semiconductor materials and devices for short wavelength opto-electronics and RF power electronics.