Surface-normal illuminated pseudo-planar Ge-on-Si avalanche photodiodes with high gain and low noise.

Germanium-on-Silicon (Ge-on-Si) avalanche photodiodes (APDs) are of considerable interest as low intensity light detectors for emerging applications. The Ge absorption layer detects light at wavelengths up to ≈ 1600 nm with the Si acting as an avalanche medium, providing high gain with low excess avalanche noise. Such APDs are typically used in waveguide configurations as growing a sufficiently thick Ge absorbing layer is challenging. Here, we report on a new vertically illuminated pseudo-planar Ge-on-Si APD design utilizing a 2 µm thick Ge absorber and a 1.4 µm thick Si multiplication region. At a wavelength of 1550 nm, 50 µm diameter devices show a responsivity of 0.41 A/W at unity gain, a maximum avalanche gain of 101 and an excess noise factor of 3.1 at a gain of 20. This excess noise factor represents a record low noise for all configurations of Ge-on-Si APDs. These APDs can be inexpensively manufactured and have potential integration in silicon photonic platforms allowing use in a variety of applications requiring high-sensitivity detectors at wavelengths around 1550 nm.

3D LIDAR imaging using Ge-on-Si single-photon avalanche diode detectors.

We present a scanning light detection and ranging (LIDAR) system incorporating an individual Ge-on-Si single-photon avalanche diode (SPAD) detector for depth and intensity imaging in the short-wavelength infrared region. The time-correlated single-photon counting technique was used to determine the return photon time-of-flight for target depth information. In laboratory demonstrations, depth and intensity reconstructions were made of targets at short range, using advanced image processing algorithms tailored for the analysis of single-photon time-of-flight data. These laboratory measurements were used to predict the performance of the single-photon LIDAR system at longer ranges, providing estimations that sub-milliwatt average power levels would be required for kilometer range depth measurements.

High performance planar germanium-on-silicon single-photon avalanche diode detectors.

Single-photon detection has emerged as a method of choice for ultra-sensitive measurements of picosecond optical transients. In the short-wave infrared, semiconductor-based single-photon detectors typically exhibit relatively poor performance compared with all-silicon devices operating at shorter wavelengths. Here we show a new generation of planar germanium-on-silicon (Ge-on-Si) single-photon avalanche diode (SPAD) detectors for short-wave infrared operation. This planar geometry has enabled a significant step-change in performance, demonstrating single-photon detection efficiency of 38% at 125 K at a wavelength of 1310 nm, and a fifty-fold improvement in noise equivalent power compared with optimised mesa geometry SPADs. In comparison with InGaAs/InP devices, Ge-on-Si SPADs exhibit considerably reduced afterpulsing effects. These results, utilising the inexpensive Ge-on-Si platform, provide a route towards large arrays of efficient, high data rate Ge-on-Si SPADs for use in eye-safe automotive LIDAR and future quantum technology applications.

One dimensional transport in silicon nanowire junction-less field effect transistors.

Junction-less nanowire transistors are being investigated to solve short channel effects in future CMOS technology. Here we demonstrate 8 nm diameter silicon nanowire junction-less transistors with metallic doping densities which demonstrate clear 1D electronic transport characteristics. The 1D regime allows excellent gate modulation with near ideal subthreshold slopes, on- to off-current ratios above 108 and high on-currents at room temperature. Universal conductance scaling as a function of voltage and temperature similar to previous reports of Luttinger liquids and Coulomb gap behaviour at low temperatures suggests that many body effects including electron-electron interactions are important in describing the electronic transport. This suggests that modelling of such nanowire devices will require 1D models which include many body interactions to accurately simulate the electronic transport to optimise the technology but also suggest that 1D effects could be used to enhance future transistor performance.

Design and fabrication of memory devices based on nanoscale polyoxometalate clusters.

Flash memory devices--that is, non-volatile computer storage media that can be electrically erased and reprogrammed--are vital for portable electronics, but the scaling down of metal-oxide-semiconductor (MOS) flash memory to sizes of below ten nanometres per data cell presents challenges. Molecules have been proposed to replace MOS flash memory, but they suffer from low electrical conductivity, high resistance, low device yield, and finite thermal stability, limiting their integration into current MOS technologies. Although great advances have been made in the pursuit of molecule-based flash memory, there are a number of significant barriers to the realization of devices using conventional MOS technologies. Here we show that core-shell polyoxometalate (POM) molecules can act as candidate storage nodes for MOS flash memory. Realistic, industry-standard device simulations validate our approach at the nanometre scale, where the device performance is determined mainly by the number of molecules in the storage media and not by their position. To exploit the nature of the core-shell POM clusters, we show, at both the molecular and device level, that embedding [(Se(IV)O3)2](4-) as an oxidizable dopant in the cluster core allows the oxidation of the molecule to a [Se(v)2O6](2-) moiety containing a {Se(V)-Se(V)} bond (where curly brackets indicate a moiety, not a molecule) and reveals a new 5+ oxidation state for selenium. This new oxidation state can be observed at the device level, resulting in a new type of memory, which we call 'write-once-erase'. Taken together, these results show that POMs have the potential to be used as a realistic nanoscale flash memory. Also, the configuration of the doped POM core may lead to new types of electrical behaviour. This work suggests a route to the practical integration of configurable molecules in MOS technologies as the lithographic scales approach the molecular limit.

Determining the electronic performance limitations in top-down-fabricated Si nanowires with mean widths down to 4 nm.

Silicon nanowires have been patterned with mean widths down to 4 nm using top-down lithography and dry etching. Performance-limiting scattering processes have been measured directly which provide new insight into the electronic conduction mechanisms within the nanowires. Results demonstrate a transition from 3-dimensional (3D) to 2D and then 1D as the nanowire mean widths are reduced from 12 to 4 nm. The importance of high quality surface passivation is demonstrated by a lack of significant donor deactivation, resulting in neutral impurity scattering ultimately limiting the electronic performance. The results indicate the important parameters requiring optimization when fabricating nanowires with atomic dimensions.

Does race affect outcomes in triple negative breast cancer?

BACKGROUND: There is discordance among studies assessing the impact of race on outcome of patients with Triple Negative Breast Cancer (TNBC). We assessed survival outcomes for African American (AA) versus Caucasian (CA) women with TNBC treated at an urban cancer center in Memphis, TN with a predominant AA patient population. METHODS: Patients with Stage I-III TNBC were identified from our breast database. Event free survival (EFS) and Breast cancer specific survival (BCSS) were the primary outcome measures. Cox proportional hazards models were fitted for EFS and BCSS. RESULTS: Of the 124 patients, 71% were AA. No significant association between race and stage (P = 0.21) or menopausal status (P = 0.15) was observed. Median age at diagnosis was significantly lower for AA versus CA women (49.5 vs. 55 years, P = 0.024). 92% of the patients received standard neo/adjuvant chemotherapy, with no significant difference in duration and type of chemotherapy between the races. With a median follow up of 23 months, 28% of AA vs. 19% of CA women had an event (P = 0.37). 3 year EFS and BCSS trended favorably towards CA race (77% vs. 64%, log rank P = 0.20 and 92% vs. 76%, P = 0.13 respectively) with a similar trend noted on multiple variable modeling (EFS: HR 0.62, P = 0.29; BCSS: HR 0.36, P = 0.18). AA women >/=50 years at diagnosis had a significantly worse BCSS than the CA women in that age group (P = 0.012). CONCLUSION: Older AA women with TNBC have a significantly worse breast cancer specific survival than their CA counterparts. Overall, there is a trend towards lower survival for AA women compared to Caucasians despite uniformity of tumor phenotype and treatment. The high early event rate, irrespective of race, underscores the need for effective therapies for women with TNBC.