University of Twente Student Theses


Dislocation engineered silicon Light Emitting Diode

Schippers, Bob (2005) Dislocation engineered silicon Light Emitting Diode.

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Abstract:Since the 60’s silicon rapidly became the dominant material due to its superior oxide quality in combination with CMOS-technology. The silicon fraction of the semiconductor market is around 95% with the remainder dominated by III–V semiconductors. Two drawbacks of silicon compared to some other III–V semiconductors are its indirect band gap and low electron mobility. Despite silicon’s indirect band gap there have been great efforts over the past decade to obtain technologically viable and efficient light emission from silicon with operating wavelengths in the range of 0.45−1.6μm (2.8−0.7eV) to cover both full color displays and fiber optics operating wavelengths of 1.3 and 1.55μm. The driving force behind silicon optics is the interconnect problem in computer chips. The electronics and computing sectors have been driven by the exponential growth in processor power and speed. This growth has been achieved by the systematic shrinking down of the transistor dimensions enabling more and more transistors to be formed in the same area of silicon thus increasing the speed and power of the chip. As the transistors need to be connected together essentially by wires referred to as metallization, there is a time delay associated with electron transport in the metallization and this time does not scale. The solution to this interconnect problem is the replacement of at least some of the metal interconnects with optical interconnect. Given the huge tool up costs in the microelectronics industry new approaches are closely compatible with silicon Ultra Large Scale Integration (ULSI) technology. The key technology for the fabrication of silicon chips is ion implantation. Dislocation engineering is based upon ion implantation and annealing to engineer defects at approximately the implantation depth that are supposed to enhance light emission out of silicon. Diode sets have been prepared for different implants and anneals to engineer respectively depth of the defects with respect to the light emitting surface area and defect density/ defect radius. By proper choice of the annealing budget the dominant defect is a so called dislocation loop. Diode sets DILED1 and DILED2 have been fabricated by boron implantation with energies in the range 40 − 100keV, annealing temperatures in the range 850 − 1100°C and doses in the range 1×1015 − 1.6×1015cm-2 to compensate for decreasing peak concentration with increasing implant energy. Diode set DIFLED has been fabricated by single, double or no silicon implants in boron diffused junction with energies in the range 0 − 450keV, annealing temperature of 950°C and each dose equal to 1×1015cm-2. DILED1, DILED2 and DIFLED I-V characteristics have been measured and light intensity measurements have been performed in the wavelength range 950 − 1300nm. Electrical parameters that have been derived and compared to estimated values are: photo current, saturation current, thermal voltage equivalent, ideality factor, junction voltage and bulk resistance. The electrical parameters have been compared to find a correlation with optical parameters peak intensity and standard deviation in peak intensity but no trends were observed. The maximum peak intensity was situated around 1154nm and belonged to diodes annealed at 1100°C originating from diode set DILED2. This maximum peak intensity was weakly dependent upon the energy range 40 − 70keV. The average deviation in peak intensity was 4.2%. This maximum peak intensity has been compared to that of a DIFLED “no silicon implant in boron diffused junction” diode that served as reference. Main conclusion: dislocation loops do not seem to enhance light intensity.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:53 electrotechnology
Programme:Electrical Engineering MSc (60353)
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