| Summary: | 碩士 === 南台科技大學 === 光電工程系 === 98 === There had been few published literatures of porous-silicon (PS) on ultra-violet (UV) photodetectors, because the optical absorption of this material ranged from visible to infrared light. Although as a wide-bandgap semiconductor due to the quantum-size effect, nano-porous-Si (NPS) also can hardly absorb UV energy due to its insufficiently large bandgap (< 2ev). In this thesis, oxidized nano-porous-Si (ONPS) that prepared by rapid-thermally oxidizing NPS thin-films was proposed for UV sensing applications.
NPS thin-films with uniformly distributed Si nano-crystallites (3nm~10nm) were firstly prepared on heavily doped p+-type (100) Si wafers by anodic etching processes with low etching current density (10mA/cm2 ). Then ONPS films were obtained from rapid-thermal-oxidation (RTO) treatment of NPS at 850℃ for 90 sec. Photo-sensing diodes were made with ONPS films as the light-absorption layers, after depositing inter-digitated aluminum (Al) electrodes on the front sides of the devices.
The optical bandgap of a NPS film was measured about 1.6ev, whereas it was raised to 3.5ev for the as-formed ONPS film after RTO processes. The photo-response spectra of a NPS film located within wavelengths from 500nm to 900nm. However, an ONPS film exhibited high photoresponsivity for incident wavelengths between 300nm and 400nm, showing it was very suitable for UV sensing applications. Furthermore, an ONPS photodiode can achieve a high photo-to-dark current ratio up to about 2000 under an incident light wavelength of 350nm while obtained quite low dark current down to 7.3A/cm2. Experimental results indicated that ONPS photodetectors had high UV sensitivity. Finally, a tentative carrier transport mechanism was proposed to illustrate the UV photoresponse processes in an ONPS structure.
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