New RP‐CVD grown ultra‐high performance selectively B‐doped pure‐Ge 20 nm QWs on (100)Si as basis material for post‐Si CMOS technology

Abstract

Magnetotransport studies at low and room temperature are presented for two‐dimensional hole gases (2DHG) formed in fully strained germanium (sGe) quantum wells (QW). Two designs of modulation doped heterostructure grown by reduced pressure chemical vapour deposition (RP‐CVD) were used and included a normal structure (doping above the Ge channel and inverted structure (doping beneath the Ge channel). The mobility (μH) for the normal structure was measured to be 1.34×106 cm2/Vs with a sheet density (ps) of 2.9×1011cm‐2at 1.5 K, and μH= 3970 cm2/Vs and ps ∼1×1011cm‐2 for room temperature, determined from simulation using the Maximum Entropy‐Mobility Spectrum Analysis (ME‐MSA) method. For the inverted structure a μH of 4.96×105 cm2/Vs and ps of 5.25×1011cm‐2was measured at 90 mK. From the temperature dependent amplitude of Shubnikov de Haas oscillations, the normal structure was found to have a very low effective mass (m*) value of 0.063 m0 and a ratio of transport to quantum lifetime (α) of ∼78. This extremely high α is indicative of the carrier transport being dominated by small angle scattering from remote impurities i.e. a sample having an extremely low background impurity level and very smooth hetero‐interfaces. The inverted structure had an m*of 0.069 m0 and α ∼29, which also indicates exceedingly high quality material. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Impact of strain on hole mobility in the inversion layer of PMOS device with SiGe alloy thin film

“…The alloy scattering, however, still plays an important role by pushing the total mobility down as the Ge mole fraction increases from pure Si before improving back to the pure Si mobility value at a higher Ge mole fraction. This leads to the characteristic 'U' shaped hole mobility curve similar to previous studies [12]. The Ge mole fraction at which Si 1− x Ge x has its total mobility equal to that of Si can be seen in the Figs.…”

“…They suggested the value of alloy potential being 0.6 eV for SiGe alloy channel materials in PMOSFET devices. The research results of Prof. Myronov in University of Warwick, UK, were similar to the HEMT (high electron mobility transistor) structure, as the number of subbands in the quantum well channel was not many [11][12][13]. In comparison, the studied elements in this research are the PMOSFET results, where the correspondent number of subbands at the inversion is a lot, the scattering among all subbands is more serious, and the calculated inversion charge density is larger than 10 13 cm −2 , which is a lot larger than its 10 11 cm −2 .…”

Activated and Metallic Conduction in p -Type Modulation-Doped Ge - Sn Devices

“…The Hall effect hole density is 4.2 × 10 11 cm −2 showing good agreement with the Shubnikovde Haas density and that there is no parallel conduction in the device structure from the surface, doping supply layer, thick Ge buffer layers, or a band of disordered low mobility carriers. The plateaus in the quantum Hall effect are narrow (< 0.3 T width at υ = 4) and are more characteristic of a low-disorder system, comparable to that in strained p-Ge, inverted-doping QWs [29].…”

“…This wafer doping design is an "inverted-doping" structure, where the modulation doping layer is between the QW and the substrate. This inverted-doping structure usually results in a lower hole mobility compared to the normally doped scheme in Ge-based devices [29] but the potential for gate leakage with Schottky surface gates is reduced significantly in the case of the inverted-doping interface.…”

Magnetotransport in p-type Ge quantum well narrow wire arrays

“…The phase coherence length in the wires is calculated from the dephasing time, s / , in a quasi-one-dimensional system 32 with where T is the measurement temperature, E F is the Fermi energy, D is the diffusion constant, and P o is the density of states in the valence band of the Ge quantum well. The hole effective mass used to determine P o has been measured to be 0.063m e in similar Ge quantum well structures, 33 where m e is the free electron mass. Using Eq.…”