Electronic and photonic devices: experimental investigations of hydrogenated amorphous silicon substrate n+/i/p+ solar cell and fundamental properties of quantum wells with cylindrical geometry and applications to electronics and photonics

Ping, Er-Xuan
Major Professor
Vikram Dalal
Committee Member
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Electrical and Computer Engineering

This thesis consists of two different parts: (I) experimental investigations of hydrogenated amorphous silicon substrate n[superscript]+/i/p[superscript]+ solar cells and, (II) fundamental properties of quantum wells with cylindrical geometry and applications to electronics and photonics;Part I. The substrate structural n[superscript]+/i/p[superscript]+ solar cells based on a-Si:H materials are fabricated by a radio frequency (RF) triode geometric plasma enhanced chemical vapor deposition (PECVD) system. The solar cells have been electrically and optically tested. Two different substrates, tin-oxide coated glass and stainless steel foil, are used. An RF magnetron sputtering system is used to deposit the indium-tin-oxide (ITO) conductive transparent film for the front contact. Semi-transparent chromium (Cr), deposited by thermal evaporation, is used as an Ohmic front contact to the boron-doped a-(Si,C):H p[superscript]+ layer. The p[superscript]+ layer was smoothly connected to the i layer by an a-(Si,C):H buffer layer in which the carbon concentration is varied. This results in an enhancement of open circuit voltage and collection of photo-generated carriers. Effects of sub ppm boron compensation in the intrinsic layer were investigated. Temperature grading in the intrinsic layer, which modifies the energy band gap, was also studied. The effects of n[superscript]+ layer on the performance of the cell are investigated. It is shown that the device with a thick n[superscript]+ layer maintains a stable efficiency. In conclusion, a technique for depositing substrate a-Si:H solar cells in a single chamber system has been developed. This process yields cells with fill factors better than 65%, open circuit voltages of 0.8 volts and short circuit currents of 10 mA/cm[superscript]2, and conversion efficiencies of 5% for non-textured stainless steel substrates. The devices made in this work show a degradation of the conversion efficiency of less than 10% under prolonged (40 hours) 1 W/cm[superscript]2 Xenon light soaking;Part II. The fundamental properties of cylindrical geometry quantum well structures have been studied theoretically. A general iteration method and transfer matrix formalism are developed. It is shown that the quantum wells with cylindrical geometry display interesting features that originate from the specific symmetry of the structure. The electronic and optical properties can be changed dramatically by the utilization of a magnetic field. The applications of the new structure include resonant tunneling devices and in-situ tunable semiconductor quantum well lasers. It is also proposed that quantum devices that operating on the basic symmetry of this structure could have performance that is less sensitive to the thermal effect. The study is of fundamental importance to the basic knowledge of quantum well structures.