Possible Realization of Near Optimum Efficiency from n-Si-Ge/p-Ge-Si DDR Hetero Structure IMPATT Diode

Avalanche breakdown in a p-n junction can generate rf negative resistance due to twin delay mechanism (Avalanche Delay associated with growth of charge bump and transit time delay caused due to time elapsed for the grown charge bump drifting through the depletion zone) leading to generation of high frequency power in IMPATT mode. With the advancement of device technology and with the motive of furtherance of device performance, replacement of homo junction of single elemental semiconductor with hetero junction, hetero structure junctions from lattice matched pair of elemental semiconductors is now being explored as supported by recent reports. The introduction of an n-Ge and p-Ge impurity bumps on either side of junction interface of a Si p-n junction, results in the formation of a n-Si-Ge/p-Ge-Si hetero structure p-n junction. The analysis of such hetero structure Impatt diode for generation of micro/mm-wave power at designed atmospheric window frequencies of 15 and 94 GHz becomes the scope of the study of this paper. The results are computed through three tier sophisticated computer algorithm indicate efficiency enhancement in case of proposed hetero structure to nearly 29% (at X-band) as against only 14% for the corresponding the homo junction diodes associated with increase of diode negative conductance by nearly two fold which in turn could enhance the rf power delivery from the hetero structure diode by many fold. Presence of low BG Ge near high field junction interface and its order high carrier ionization rate (compared to Si) localizes the avalanche zone to below 10% of the depletion zone and thereby pushes the device efficiency and value of negative conductance. However the performance of complementary n-Ge-Si/p-Si-Ge hetero structure remains close to Si or Ge homo junction. The results are highly encouraging which may make Si-Ge-Si Hetero Structure Diode as a prospective microwave generator.