S. Nakamura ( Nichia Chemical Industries, Japan) presented one of the plenary talks titled "First III-V nitride based violet laser diodes". He presented the recent results on blue and blue-green LEDs and violet/UV color lasers. The InGaN MQW laser diode had a threshold current of 610mA (density 8.7 kA/cm2). The differential quantum efficiency was 17% per facet and the pulsed output power was 57 mW per facet at a current of 700mA. The operating voltage was 21V. There were demonstrations of large panel color displays, violet/UV lasers during the talk.
There were six papers during the first session on GaN which was held on tuesday morning. D. Kapolnek (UCSB, USA) presented results on selective area MOCVD growth of GaN on patterned GaN/Sapphire substrates. Circular patterns were delineated on GaN/sapphire substrates using SiO2 masks. Under proper conditions, GaN growth was observed only on exposed regions. The selectively grown layers are of pyramid shaped, with sharp tips at the surface. These were tested for possible use in field emission displays. Preliminary results on an array of pyramids used as field emitters have been reported. This paper received the best student paper award.
S. Tanaka (The Institute of Physical and Chemical Research, Japan) has reported that ultra thin buffer layer (about 1nm) of AlN is needed to get high quality GaN on SiC substrates. Thin (less than 5 nm) AlN layer grows pseudomorphically and the surface of AlN is very smooth (as shown by AFM) and the subsequent GaN grown on this thin AlN/SiC had dislocation density in the range 17-18 cm-2. The substrate should be atomically smooth without any steps, indicating that exact (0001) face is ideal. Thicker buffer layers of AlN results in rougher GaN caused by the three dimensional growth of AlN. Ambacher (Walter Schottky Institute, Germany) reported on the growth of high quality AlGaN and AlN using tritertiarybutylaluminum as the Al source instead of the more common source trimethyaluminum. K. Pakula (Institute of Experimental Physics, Warsaw) presented results of MOCVD growth of GaN and GaAlN on single crystal GaN. Homoepitaxial GaN had much narrower PL FWHM ( about 1 meV) compared to GaN grown on sapphire. In addition, growth on N-terminated bulk GaN are much smoother compared to those grown on Ga-terminated surface. A research staff from Advanced Technology Materials, USA presented comparative results of AlGaN/GaN heterostructure growth on SiC and sapphire substrates. The electron mobilities and sheet carrier concentrations of several Al0.15Ga0.85N/GaN heterostructures grown on sapphire and SiC substrates were compared. The highest electron mobility of 7400cm2/Vs was measured when the structure was grown on SIC substrate. Additional characterizations (such as SDH measurements) on the heterostructures were presented during the talk.
The morning session on Wednesday was opened by a talk by S. Denbaars (UCSB, USA) on the growth of InGaN epitaxial layers. Lifetimes of the order of 300ps was measured in InGaN films. For InGaN QW, quantization was observed only for QW thicknesses below 35A. Very high V/III ratio (V/III ratio of over 10,000) was found to be necessary to get In-droplet-free films This was followed by a talk by V. Harle (University of Stuttgart) on the GaN-GaInN growth by low pressure MOVPE. One interesting result was that the In incorporation in InGaN increased as the reactor pressure was decreased. Two more papers in this session were on the growth of GaPN and InAsN. H. Yaguchi (University of Tokyo) presented the PL and PLE spectra of GaP(1-x)N(x) layers grown by MOVPE. A systematic PL studies of several GaPN layers with x varying from 0.0 to 2% were presented, confirming the earlier observation that there is a large bandgap bowing in GaP-GaN systems. S. Sakai (University of Tokushima) presented the summary of their efforts to introduce N to InAs. Using conventional MOVPE, high percentage of nitrogen incorporation was found to be difficult. Results on plasma-cracked N2 was also presented. All the layers were discontinuous when grown on GaAs substrates.
Following the above session, about 10 papers were displayed as posters. B. Beaumont (CNRS, France) compared the results of GaN obtained using several nitrogen precursors, including triethylamine, terbutylamine, NH3, plasma activated NH3 and plasma activated N2. The best results were obtained with NH3. Triethylamine did not produce any GaN. A. Wickenden (NRL, USA) presented a systematic x- ray diffraction studies on GaN and sapphire and the effects of pre- growth thermal treatments on sapphire on the layer properties. T.F. Kuech (University of Wisconsin) provided experimental information on the high temperature gas phase reactions between TMG and NH3 using in-situ mass spectrometry. Using deuterium and deuterated ammonia, they studied the decomposition pathways for TMG in H2 and ammonia. Y. Ohuchi and his group (Mitsubishi Cable Industries, Japan) provided the results on the use of tetraethylsilane as n type dopant and bis(ethylcyclopentadienylmagnesium) as p type dopant. They found that the results are similar to the results obtained using silane and CP2Mg. The advantage of these precursors is that both are liquids at room temperature so that transport of these to the reactor is easier.
The papers from the conference will be published in a special issue of J. Crystal Growth.
Summarized by:
Ishwara Bhat ECSE Department, RPI Troy, NY 12180-3590 Ph: 518-276-2786 Fax: 518-276-6261 Email: bhat@ecse.rpi.edu