Si-based Blue Light Emitting Diode

UNDER AN ONGING SDIO-FUNDED SBIR PROGRAM, SPIRE RECENTLY DEMONSTRATED THE FIRST Si-BASED VISIBLE LIGHT-EMITTING DIODES (LED), OBTAINING COLORS RANGING FROM RED THROUGH YELLOW. THESE Si DEVICES WERE PRODUCED AS NANODIMENSIONAL STRUCTURES FROM P-TYPE SUBSTRATES BY ELECTROCHEMICAL ETCHING. THE SHORTER WAVELENGTHS RESULTED FROM REDUCING THE STRUCTURE SIZE TO THE 1-2 NM LEVEL. HOWEVER, CALCULATIONS OF THE CONFINEMENT ENERGIES OF ELECTRONS AND HOLES IN Si NANOSTRUCTURES INDICATE THAT THE CRYSTAL DIMENSIONS REQUIRED FOR BLUE EMISSION ARE GENERALLY TOO SMALL TO BE STABLE OVER EXTENDED PERIODS. WE PROPOSE THAT THE CONSTRAINTS ON MICROCRYSTALLINE DIMENSIONS FOR PRODUCING BLUE LEDs CAN BE RELAXED BY CREATING ALLOYS OF Si WHICH INSTRINSICALLY POSSESS LARGER ENERGY GAPS. SIGNIFICANTLY, SINCE CRYSTALLINE CARBON (DIAMOND) HAS A LARGE BANDGAP (5.5 eV), ALLOYS OF SEVERAL PERCENT C IN Si WILL READILY INCREASE THE BASE BANDGAP; HOWEVER, MISMATCHES IN UNIT CELL DIMENSIONS WILL BE DETRIMENTAL, UNLESS GERMANIUM ATOMS ARE ALSO INTRODUCED TO COMPENSATE. WE PREDICT THAT THE OPTICAL EMISSION PROPERTIES WILL BE AFFECTED PREDOMINATELY BY C, ALLOWING FORMATION OF A NEW MATERIAL EXHIBITING QUANTUM CONFINEMENT EFFECTS PLUS DIMENSIONAL STABILITY. IN PHASE I, WE SHALL USE SPIRE'S PROVEN NON-EQUILIBRIUM DEPOSITION CONDITIONS, ALREADY APPLIED TO Si(1-x)Ge(x), TO ASSURE THE FORMATION OF Si(1-x-y)Ge(x)C(y) ALLOYS, 0,x,y<5%, WITHOUT SUFFERING THE FORMATION OF UNDESIRABLE SECOND PHASES, AND DEMONSTRATE BLUE PHOTOLUM-INESCENCE IN ETCHED STRUCTURES. WE WILL DEMONSTRATE BLUE ELECTROLUM-INESCENCE IN POROUS SiGeC-BASED DEVICES IN PHASE II.