Song Tong

Normal-incidence Ge quantum-dot photodetectors at 1.5 μm based on Si substrate

Coherent Ge quantum dots embedded in Si spacing layers were grown on Si substrate by molecular-beam epitaxy in the Stranski–Krastanov mode. Photoluminescence measurement showed a Ge-dot-related peak at 1.46 μm. p-i-n photodiodes with the intrinsic layer containing Ge dots were fabricated, and current–voltage (I–V) measurement showed a low dark current density of 3×10−5 A/cm2 at −1 V. A strong photoresponse at 1.3–1.52 μm originating from Ge dots was observed, and at normal incidence, an external quantum efficiency of 8% was achieved at −2.5 V.

High-quality Ge films on Si substrates using Sb surfactant-mediated graded SiGe buffers

High-quality Ge films were grown on Si substrates by solid-source molecular beam epitaxy using SiGe graded layer and Sb surfactant-mediation technique. Transmission electron microscopy measurements show that samples grown using this method have a lower threading dislocation density than those grown by other typical methods, such as grading at high temperature (700 °C) only, grading at intermediate temperature (510 °C) only, and the use of low temperature Si buffer. A relaxed Ge film on a 4-μm-thick graded buffer was grown and shown to have a threading dislocation density of 5.4×105 cm−2 and surface roughness of 35 A. Ge p–i–n diodes were fabricated and tested. Under a reverse bias of 1 V, the p–i–n Ge mesa photodiodes exhibit a very low dark current density of 0.15 mA/cm2.

Normal incidence intersubband photoresponse from phosphorus δ-doped Ge dots

Normal incidence mid- and far-infrared photodetectors based on phosphorus δ-doped Ge dots were achieved on Si (100) substrates. Ge dots embedded in Si spacer layers were grown by molecular-beam epitaxy in the Stranski–Krastanov mode. The heavily doped (5×1019cm−3) Ge dot in the intrinsic Si matrix forms self-consistent potential wells in the conduction band for the ionized electrons. Photoresponse was demonstrated for an n‐i‐n structure in both the mid- and far-infrared wavelength ranges. The nonvanishing normal incidence response was due to the presence of nonzero off-diagonal terms for the electron mass tensor in Ge.

Nano-patterned Growth of Ge Quantum Dots for Infrared Detector Applications

Quantum dot infrared photodetectors (QDIPs) have been studied widely for normalincidence infrared detection. The 3D confinement provided by quantum dots allows for the elimination of gratings that are typically required for normal-incidence detection in quantum well infrared photodetectors (QWIPs). Furthermore, the growth of Ge dots on Si substrates offers the potential for integration with existing CMOS platforms. To date, however, Ge QDIPs have typically been grown epitaxially by Stranski-Krastonov growth – producing pancake-like dots with base dimensions of 50-100 nm, heights of 7-10 nm, and an aerial dot density of 10 9 -10 10 cm -2 . Such dots have poor lateral confinement, causing them to have non-ideal normalincidence absorption characteristics, similar to quantum wells. In this work, we demonstrate infrared absorption in Ge dots with base dimensions of approximately 15 nm. These dots are epitaxially grown on pre-patterned Si substrates, with an aerial dot density of approximately 10 11 cm -2 . The substrates are prepared by using diblock copolymers to create a nano-pattern on the substrate surface which is transferred to the substrate by dry etching. The size of this pattern determines the base dimensions of the Ge dots. After growth, these dots are then tested for their infrared absorption properties using Fourier Transform Infrared (FTIR) Spectroscopy. The normal-incidence absorption of the dots can be studied with FTIR by varying the polarization angle of the infrared light. We present FTIR absorption spectra for samples grown with various conditions (e.g., different dot doping levels, numbers of layers, and dot base dimensions) and investigate the effects of different growth conditions on infrared absorption properties. We also report on the normal-incidence absorption characteristics of these dots by presenting absorption spectra for various polarization angles of infrared light.

Microstructure and optical properties of Ge(Si) dots grown on Si

The microstructural, luminescence properties and photoresponse of multilayer Ge(Si) quantum dots grown on Si (100) substrates are studied. The strain and composition of the dots are studied by synchrotron-radiation x-ray. The dots are found to be Si0.58Ge0.42 alloy with 50% strain relaxed in average. The photoluminescence from the dots is observed up to room temperature. The thermal stability of the quantum dots is studied. P-i-n structures are grown with Ge(Si) dots embedded in the i-layer for photodetection investigation. The photoresponse wavelength of Ge(Si) dots covers the wavelength range of 1.3-1.52 mm and relatively high external quantum efficiency is obtained.