Germanium: The Past and Possibly a Future Material for Microelectronics

Abstract

Germanium possesses higher bulk mobilities than silicon and was used for the first transistors. However, by the 1960s its use was largely supplanted with Si due largely to Si's high quality thermal oxide. Today, with the 45 nm technology node in production, high k dielectrics are beginning to replace SiO2 in the gate, and as such, one of the key reasons for using Si is no longer as relevant. This, combined with performance concerns for Si based devices for and beyond the 22 nm node has made Ge a worthy area for research for high performance devices. In this paper, we give an overview of some of the major issues for Ge MOSFETs, illustrating recent progress using data from IMEC. Key results include a factor of 10 reduction in threading dislocations for epi Ge on Si by the use of an ~850{degree sign}C anneal, the first successful use of As halo implants, progress on optimization of activation anneals, the use of a thin epitaxial Si passivation and its impact on threshold voltage, a 2-step anneal NiGe process flow to drastically reduce defects, and the importance of a hydrogen anneal following metallization.

Crystalline SrZrO3 deposition on Ge (001) by atomic layer deposition for high-k dielectric applications

“…[25][26][27] Compared to Si, the electron mobility and hole mobility for Ge are 3900 vs 1400 cm 2 /V s and 1900 vs 500 cm 2 /V s, respectively, which makes Ge viable as a next generation channel material. 27,28 In addition, Ge has a more unstable oxide than Si, making it easier to remove the native oxide to achieve a clean surface. [29][30][31] A high D it can affect the channel mobility and negate the inherent mobility advantages of Ge.…”

Gate‐Tunable Negative Differential Resistance in Next‐Generation Ge Nanodevices and their Performance Metrics

“…[ 4–6 ] In this context, low‐dimensional Ge structures such as nanomembranes [ 7,8 ] and vapor‐liquid‐solid [ 9 ] (VLS) grown nanowires [ 10,11 ] (NWs), exhibiting unique electrical [ 4,10,12 ] and optical [ 13–15 ] properties departing from their bulk counterparts, are considered key building blocks in a “More than Moore” approach extending device performances beyond the limits imposed by miniaturization. [ 16,17 ] In this respect, a highly interesting transport mechanism is the transferred electron effect, enabling negative differential resistance (NDR) following the Ridley–Watkins–Hilsum theory. [ 18 ] Also known as the Gunn‐effect in GaAs [ 19 ] and GaN nanocrystals, [ 20 ] this effect is based on applying sufficiently high electric fields, resulting in electrons from the energetically favorable conduction band valley, characterized by a low effective mass, being transferred to a heavy mass valley nearby.…”

Basic single-event mechanisms in Ge-based nanoelectronics subjected to terrestrial atmospheric neutrons

“…Germanium was the semiconductor material of first-generation transistors in the late 1940s and early 1950s before it was replaced by silicon for large scale-area microelectronics [1]. However, using germanium instead of silicon as transistor material would enable more performant transistors and faster chips because of its higher mobility values for electrons and holes than those of silicon.…”