Pattern formation in planar dc-driven semiconductor-gas discharge devices: two mechanisms

The spatial and spatio-temporal patterning of the luminance distribution in laterally extended dc-driven gas-discharge systems with a semiconductor high-ohmic electrode is investigated. It is experimentally verified that a primary instability, via which a pattern is generated in the device, may be due to the active role of both the semiconductor component and the gas-discharge layer. Under the experimental conditions, formation of patterns at the expense of the semiconductor electrode is caused by the N-type negative differential conductivity (NDC) of the latter (if one plots the discharge current, 1, as a function of the applied voltage, U). The critical voltage drop on the semiconductor at which NDC arises depends on the temperature in an essential way. Thus, by changing the temperature of the device, one can shift the critical supply voltage that corresponds to the onset of patterning of electrical current in the system. At conditions where the semiconductor component reveals a monotonic current-voltage characteristic, the patterning of the electric current in the device call be attributed to the active properties of the gas discharge. Presumably, it is the S-type NDC of the gas that is responsible for the formation of spatial structures in this case. The observed scenarios of pattern formation are qualitatively different for these two mechanisms.