A diode with Sb-doped p-type ZnO, MgZnO/ZnO/MgZnO double heterojunction, and undoped n-type ZnO layers was
grown on c-plane sapphire substrate by plasma-assisted molecular-beam epitaxy. Hall effect measurement showed that
the top p-type Sb-doped ZnO layer has a hole concentration of 1×1017cm-3. Mesa geometry light emitting diodes were
fabricated with Au/Ni and Au/Ti Ohmic contacts on top of the p-type and n-type layers, respectively. Strong ultraviolet
emission was achieved, which yielded an output power of 457 nW at 140 mA. The drastic enhancement of the output
power is attributed to carrier confinement in the good-quality intrinsic layer of the double heterojunction. The spatial
distribution of light emission was characterized.
Sb-doped p-type ZnO films were grown on n-Si (100) by electron cyclotron resonance (ECR)-assisted molecular-beam epitaxy (MBE). Room temperature Hall effect measurements reveal that a heavily Sb-doped ZnO sample exhibits a low resistivity of 0.2 Ω cm, high hole concentration of 1.7×1018 cm-3, and high mobility of 20.0 cm2/V s. Low-temperature photoluminescence (PL) measurements show an Sb-associated acceptor-bound exciton (AoX) emission exists at 3.358 eV at 8.5 K. The acceptor energy level of the Sb dopant is estimated to be 0.14 eV above the valence band. Based on these electrical and optical properties, p-n hetero- and homojunction photodetectors employing Sb-doped p-type ZnO films were designed and fabricated. The heterojunction photodiode consists of Sb-doped p-type ZnO grown on n-Si (100) substrate. An Sb-doped p-type ZnO layer with an n-type Ga-doped ZnO layer was grown on a p-Si (111) substrate to form the homojunction. Current-Voltage (I-V) characterizations reveal rectifying characteristics. Good photoresponse to UV light has been demonstrated for both hetero and homojunction photodetectors.
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.
The development of Si-based photodetectors is very important due to their compatibility with the state-of-the-art Si planar technology. Photodetectors based on Ge quantum dots were studied. Three p-i-n structures containing Ge dots were grown by molecular beam epitaxy in Stranski-Krastanov mode. The dots were grown embedded in Si spacing layers on Si (100) substrates. The nominal Ge growth thickness in each layer was 1.2, 1.5 and 1.8 nm for the three samples, respectively. Photoluminescence measurement showed that the Ge dot related peak shift to lower energy with increasing the dot layer thickness. The materials were processed into p-i-n photodiodes with conventional processing methods. I-V measurement showed a low dark current density of 3x10-5A/cm2 at -1 V. A strong photoresponse at 1.3-1.55 mm originating from Ge dots was observed. The response peak shifts with the Ge growth thickness. At normal incidence, an external quantum efficiency of 8% was achieved at 2.5 V. The dot layers were considered to trap the light in the intrinsic region, and thus increase the absorption.
This paper reports the growth, fabrication and characterization of integrated Ge detectors with rib waveguides based on SOI technology. The MBE Ge diode structures were first grown on different graded buffers on SOI wafers. These structures were then fabricated into individual and integrated diodes with various kinds of rib waveguides. Analysis of the performance of the integrated detectors indicates that Ge detectors with quantum efficiency over 70% can be achieved at 1.55um. Major obstacle for practical applications of these Ge detectors will be discussed.
Mid-infrared absorption in boron-doped and modulation boron- doped self-assembled Ge quantum dots grown on (001) oriented Si substrates is reported for the first time in this paper. The structures, which were grown by a solid source molecular beam epitaxy system, are composed of 20 or 30 periods of Ge dot layers and Si spacer films. The structural properties of the multilayers and some uncapped Ge dots on sample surface were tested by cross-sectional transmission electron and atomic force microscopes, respectively. Through use of Fourier transform infrared and Raman spectrometers, infrared absorption signals peaking in the mid-infrared range were observed. The absorption is strongly polarized along the growth axis of the samples. Experimental and theoretical analysis suggests that the mid-infrared response be attributed to intraband transitions in the valence band of the Ge quantum dots. This study demonstrates the application potential of these kinds of Ge/Si quantum dot multilayer structures for developing mid-infrared photodetectors.