In this paper the characterization of different masking materials for the fabrication of flow channels or thin diaphragms in aluminosilicate glass substrates (Corning 1737) is presented. Materials such as photoresist, polysilicon and gold were investigated with concentrated hydrofluoric acid, HF 48% used as an isotropic etchant. The use of single material masks restricts the useable etch depth to less than 250 µm. Surface and material imperfections result in weaknesses in the masking layer and subsequent penetration by the etchant. An etch depth of greater than 300 µm was achieved using a combination of thick SU-8 photoresist and polished polycrystalline silicon as the masking material. The two materials act as double protection to the glass substrate and the etch depth obtained is approximately three to six times larger than those published for standard photoresist or SU-8 etch mask.

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Abstract-Producing an electrically pumped silicon-based laser at terahertz frequencies is gaining increased attention these days. This paper reviews the recent advances in the search for a siliconbased terahertz laser. Topics covered include resonant tunneling in p-type Si/SiGe, terahertz intersubband electroluminescence from quantum cascade structures, intersubband lifetime measurements in Si/SiGe quantum wells, enhanced optical guiding using buried silicide layers, and the potential for exploiting common impurity dopants in silicon such as boron and phosphorus to realize a terahertz laser.

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There has been considerable interest in using impurity dopants in silicon, such as boron and phosphorus, since it was demonstrated that such materials can show emission in the THz region of the electromagnetic spectrum. The measured temperature dependence of these transitions in this letter shows that the most optimistic maximum operating temperature of such an impurity-based laser is 90 K. In a real device with current flowing and associated Joule heating, the actual operating range is likely to be much narrower and it is therefore unlikely that such a device would have a maximum operating temperature above 40 K.