SI-BASED BLUE LIGHT-EMITTING DIODE

SPIRE RECENTLY FABRICATED THE FIRST YELLOW- AND ORANGE-EMITTING HETEROJUNCTIO LIGHT-EMITTING DIODE (LED) BASED ON SILICON. THESE DEVICES WERE FABRICATED BY DEPOSITING A TRANSPARENT N-TYPE SEMICONDUCTOR (INDIUM-TIN-OXIDE) ON THE POROUS SURFACE OF ELECTROCHEMICALLY-ETCHED P-TYPE SI WAFERS. THE KEY TO THE VISIBLE EMISSION IS BELIEVED TO BE THE QUANTUM CONFINEMENT PHENOMENON IN THE NANOMETER-SIZED SI CRYSTALLITES IN THE POROUS SI LAYES. AS CRYSTALLITES GET SMALLER, THE EMISSION SPECTRUM SHIFTS TO SHORTER WAVELENGTHS (BLUE SHIFT). HOWEVER, SPIRE CORPORATION HS NOTED THAT SI CRYSTALLITES WITH LIGHT EMISSION BELOW YELLOW WAVELENGTHS ARE PHYSICALLY TOO FRAGILE AND SUSCEPTIBLE TO ENVIRONMENTAL EFFECTS AND THUS ARE NOT SUITABLE FOR DEVICE FABRICATION. THEY ARE NOW RESEARCHING A UNIQUE SOLUTION TO THE ABOVE PROBLEM; SINCE CRYSTALLINE CARBON (DIAMOND) HAS A LARGE BANDGAP OF 5.47 EV, ALLOYS OF ONLY A FEW PERCENT C IN SI WILL READILY INCREASE THE BASE BANDGAP OF THE NEW MATERIAL INTO THE RANGE WHERE QUANTUM STRUCTURES OF STABLE DIMENSIONALITY CAN BE PREPARED. THEY ARE USING NON-EQUILIBRIUM DEPOSITION CONDITIONS TO ASSURE EPITAXIAL GROWTH OF SI1-XCX ALLOYS WITHOUT THE FORMATION OF SIC PHASE. RESEARCHERS ARE USING THE CHEMICAL VAPOR DEPOSITION (CVD) PROCESS TO GROW EPITAXIAL SI1-XCX LAYERS ON SI SUBSTRATES AT LOW TEMPERATURES. THESE LAYES ARE THEN ELECTROCHEMICALLY-ETCHED TO PRODUCE POROUS LAYES CAPABLE OF LIGHT EMISSION IN THE BLUE WAVELENGTH RANGE. THE MATERIAL AND STRUCTURAL QUALITY OF THE EPITAXIAL AND POROUS LAYES WILL BE EVALUATED USING VARIOUS CHARACTERIZATION TECHNIQUES. THE BLUE PHOTOLUMINESCENCE IN POROUS SI1-XCX LAYES WILL BE DEMONSTRATED.