Direct Bandgap Cross-over Point of Ge\u3csub\u3e1-y\u3c/sub\u3eSn\u3csub\u3ey\u3c/sub\u3e Grown on Si Estimated through Temperature-dependent Photoluminescence Studies

Epitaxial Ge1-ySny (y = 0%–7.5%) alloys grown on either Si or Ge-buffered Si substrates by chemical vapor deposition were studied as a function of Sn content using temperature-dependent photoluminescence (PL). PL emission peaks from both the direct bandgap (Γ-valley) and the indirect bandgap (L-valley) to the valence band (denoted by ED and EID, respectively) were clearly observed at 125 and 175 K for most Ge1-ySny samples studied. At 300 K, however, all of the samples exhibited dominant ED emission with either very weak or no measureable EID emission. At 10 K, ED is dominant only for Ge1-ySny with y \u3e 0.052. From the PL spectra taken at 125 and 175 K, the unstrained indirect and direct bandgap energies were calculated and are plotted as a function of Sn concentration, the results of which show that the indirect-to-direct bandgap transition occurs at ∼6.7% Sn. It is believed that the true indirect-to-direct bandgap cross-over of unstrained Ge1-ySny might also take place at about the same Sn content at room temperature. This observation suggests that these Ge1-ySny alloys could become very promising direct bandgap semiconductor materials, which will be very useful for the development of various new novel Si- and Ge-based infrared optoelectronic devices that can be fully integrated with current technology on a single Si chip

Temperature-dependent photoluminescence of Ge/Si and Ge 1-ySn y/Si, indicating possible indirect-to-direct bandgap transition at lower Sn content

Temperature (T)-dependent photoluminescence (PL) has been investigated for both p-Ge and n-Ge1-ySny films grown on Si substrates. For the p-Ge, strong direct bandgap (ED) along with weak indirect bandgap related (EID) PL at low temperatures (LTs) and strong ED PL at room temperature (RT) were observed. In contrast, for the n-Ge1-ySny, very strong dominant EID PL at LT and strong ED PL were observed at RT. This T-dependent PL study indicates that the indirect-to-direct bandgap transitions of Ge1-ySny might take place at much lower Sn contents than the theory predicts, suggesting that these Ge1-ySny could become very promising direct bandgap semiconductors

Observation of Heavy- and Light-hole Split Direct Bandgap Photoluminescence from Tensile-strained GeSn (0.03% Sn)

Temperature- (T-) and laser power-dependent photoluminescence (PL) measurements have been made for the tensile-strained, undoped GeSn (0.03% Sn) film grown on Si substrate. The PL results show not only clear strain-split direct bandgap transitions to the light-hole (LH) and heavy-hole (HH) bands at energies of 0.827 and 0.851 eV at 10 K, respectively, but also clearly show both strong direct and indirect bandgap related PL emissions at almost all temperatures, which are rarely observed. This split of PL emissions can be directly observed only at low T and moderate laser power, and the two PL peaks merge into one broad PL peak at room temperature, which is mainly due to the HH PL emission rather than LH transition. The evolution of T-dependent PL results also clearly show the competitive nature between the direct and indirect bandgap related PL transitions as T changes. The PL analysis also indicates that the energy gap reduction in Γ valley could be larger, whereas the bandgap reduction in L valley could be smaller than the theory predicted. As a result, the separation energy between Γ and L valleys (∼86 meV at 300 K) is smaller than theory predicted (125 meV) for this Ge-like sample, which is mainly due to the tensile strain. This finding strongly suggests that the indirect-to-direct bandgap transition of Ge1−ySny could be achieved at much lower Sn concentration than originally anticipated if one utilizes the tensile strain properly. Thus, Ge1−ySny alloys could be attractive materials for the fabrication of direct bandgap Si-based light emitting devices

Complementary Metal-oxide Semiconductor-compatible Detector Materials with Enhanced 1550 nm Responsivity via Sn-doping of Ge/Si(100)

Previously developed methods used to grow Ge1−ySny alloys on Si are extended to Sn concentrations in the 1019−1020 cm−3 range. These concentrations are shown to be sufficient to engineer large increases in the responsivity of detectors operating at 1550 nm. The dopant levels of Sn are incorporated at temperatures in the 370–390 °C range, yielding atomically smooth layers devoid of threading defects at high growth rates of 15–30 nm/min. These conditions are far more compatible with complementary metal-oxide semiconductor processing than the high growth and processing temperatures required to achieve the same responsivity via tensile strain in pure Ge on Si. A detailed study of a detector based on a Sn-doped Ge layer with 0.25% (1.1 × 1020 cm−3) Sn range demonstrates the responsivity enhancement and shows much better I-V characteristics than previously fabricated detectors based on Ge1−ySny alloys with y = 0.02

Degenerate Parallel Conducting Layer and Conductivity Type Conversion Observed from \u3ci\u3ep\u3c/i\u3e-Ge\u3csub\u3e1 - y\u3c/sub\u3eSn\u3csub\u3ey\u3c/sub\u3e (y = 0.06%) Grown on \u3ci\u3en\u3c/i\u3e-Si Substrate

Electrical properties of p-Ge1−ySny (y = 0.06%) grown on n-Si substrate were investigated through temperature-dependent Hall-effect measurements. It was found that there exists a degenerate parallel conducting layer in Ge1−ySny/Si and a second, deeper acceptor in addition to a shallow acceptor. This parallel conducting layer dominates the electrical properties of the Ge1−ySny layer below 50 K and also significantly affects those properties at higher temperatures. Additionally, a conductivity type conversion from p to n was observed around 370 K for this sample. A two-layer conducting model was used to extract the carrier concentration and mobility of the Ge1−ySny layer alone

Luminescence Mechanisms in Quaternary Al\u3csub\u3ex\u3c/sub\u3eIn\u3csub\u3ey\u3c/sub\u3eGa\u3csub\u3e1-x-y\u3c/sub\u3eN Materials

Low-temperature photoluminescence investigations have been carried out in the quaternary AlInGaN epilayers and AlInGaN/AlInGaN multiple quantum wells (MQWs) grown by pulsedmetalorganic chemical-vapor deposition (PMOCVD). With increasing excitation power density, the emission peaks in both AlInGaN epilayers and MQWs show a strong blueshift and theirlinewidths increase. The luminescence of the samples grown by PMOCVD is attributed to recombination of carriers/excitons localized at band-tail states. We also demonstrate theluminescence properties of AlInGaN and AlGaN materials grown by a pulsed atomic-layerepitaxy and conventional MOCVD, respectively

Time-Resolved Photoluminescence of Quaternary AlInGaN-Based Multiple Quantum Wells

Time-resolvedphotoluminescence(PL)dynamics has been studied in AlInGaN/AlInGaN multiple quantum wells(MQWs) grown by a pulsed metalorganic chemical vapor deposition (PMOCVD) procedure. The PL decay kinetics was found to be sensitive to the emission energy and temperature. The PL decay time increases with decreasing emission energy, which is a characteristic of localized carrier/exciton recombination due to alloy fluctuations. Its temperature dependence shows radiative recombination to be the dominant process at low temperatures, indicating a high quality of PMOCVD grown quaternary AlInGaN MQWs and establishing them as promising structures for the active region of deep ultraviolet light emitting diodes

Rapid Prenatal Diagnosis of Down Syndrome Using Quantitative Fluorescent PCR in Uncultured Amniocytes

Rapid prenatal diagnosis of common chromosome aneuploidies have been successful through quantitative fluoresent PCR (QF-PCR) assays and small tandem repeat (STR) markers. The purpose of our study was to investigate the clinical feasibility for rapid prenatal detection of Down syndrome using the quantitative fluorescent PCR in uncultured amniocytes. DNA was extracted from uncultured amniotic fluid of normal karyotype (n=200) and of Down syndrome (n=21). It was amplified using QF-PCR with four STR markers located on chromosome 21. Among normal samples, the ranges of diallelic peaks for at least one STR marker were 1.0-1.3 for D21S11, 1.0-1.4 for D21S1411 and 1.0-1.5 for D21S1270. Down syndrome samples showed trisomic triallelic patterns or trisomic diallelic patterns. The sensitivity, specificity, and efficiency of the assay for detecting Down syndrome were 95.4%, 100%, and 99.5%, respectively. Rapid prenatal diagnosis of Down syndrome using QF-PCR is a reliable technique that aids clinical management of pregnancy

Manipulation of Photoelectrochemical Water Splitting by Controlling Direction of Carrier Movement Using InGaN/GaN Hetero-Structure Nanowires

We report the improvement in photoelectrochemical water splitting (PEC-WS) by controlling migration kinetics of photo-generated carriers using InGaN/GaN hetero-structure nanowires (HSNWs) as a photocathode (PC) material. The InGaN/GaN HSNWs were formed by first growing GaN nanowires (NWs) on an Si substrate and then forming InGaN NWs thereon. The InGaN/GaN HSNWs can cause the accumulation of photo-generated carriers in InGaN due to the potential barrier formed at the hetero-interface between InGaN and GaN, to increase directional migration towards electrolyte rather than the Si substrate, and consequently to contribute more to the PEC-WS reaction with electrolyte. The PEC-WS using the InGaN/GaN-HSNW PC shows the current density of 12.6 mA/cm2 at −1 V versus reversible hydrogen electrode (RHE) and applied-bias photon-to-current conversion efficiency of 3.3% at −0.9 V versus RHE. The high-performance PEC-WS using the InGaN/GaN HSNWs can be explained by the increase in the reaction probability of carriers at the interface between InGaN NWs and electrolyte, which was analyzed by electrical resistance and capacitance values defined therein