Nien-Tze Yeh

In0.6Ga0.4As/GaAs quantum-dot infrared photodetector with operating temperature up to 260 K

A high-sensitivity In0.6Ga0.4As/GaAs quantum-dot infrared photodetector (QDIP) with detection wave band in 6.7–11.5 μm and operating temperature up to 260 K under normal incident illumination has been demonstrated. The peak detection wavelength shifts from 7.6 to 8.4 μm when the temperature rises from 40 to 260 K. The background limited performance (BLIP) detectivity (DBLIP*) measured at Vb=−2.0 V, T=77 K, and λp=7.6 μm was found to be 1.1×1010 cm Hz1/2/W, with a corresponding responsivity of 0.22 A/W. The high operating temperature is attributed to the very low dark current and long carrier lifetime in the quantum dots of this device. The results show that this QDIP can operate at high temperature without using the large band gap material such as AlGaAs or InGaP as blocking barrier to reduce the device dark current.

Tuning the energy levels of self-assembled InAs quantum dots by rapid thermal annealing

We studied the photoluminescence spectra of rapid-thermal-annealed self-assembled InAs quantum dots at 10 K. For annealing temperatures ranging from 700 to 950 °C, we observed a blueshift in the interband transition energies, a decrease in the intersublevel spacing energies, and a narrowing of photoluminescence linewidths. In this letter, we demonstrate that the tuning of the InAs quantum dots interband transition and intersublevel spacing energies can be achieved by 30 s of rapid thermal annealing. The relation between interband transition energy changes and the intersublevel spacing energies is found to be linear, with a slope close to the ratio of the dots’ height to their diameter.

Matrix dependence of strain-induced wavelength shift in self-assembled InAs quantum-dot heterostructures

We report on the matrix-dependent strain effect in self-assembled InAs quantum-dot heterostructures using photoluminescence measurements. A series of samples were prepared to examine the effect of quantum dot position with respect to the so-called strain-reducing layer (SRL). Since the SRL reduces the residual hydrostatic strain in the quantum dots, long emission wavelength of 1.34 μm is observed for the InAs quantum dots with an In0.16Ga0.84As SRL. The dependence of the emission wavelength on the thickness of the cap layer on SRL also indicates the importance of the role of matrix in the strain relaxation process of the dots. Using In0.16Al0.84As instead of In0.16Ga0.84As as the SRL, a blueshift in wavelength is observed because the elastic stiffness of In0.16Al0.84As is higher than that of In0.16Ga0.84As and less strain is removed from the dots with In0.16Al0.84As SRL.

Thermal reliability and characterization of InGaP Schottky contact with Ti/Pt/Au metals

Abstract We present the characteristics of Ti/Pt/Au Schottky contacts on wide bandgap InGaP semiconductors with surface pre-treatment before Schottky contact deposition, and investigate the influence of post heat treatment on Schottky diodes. With the pre-deposition surface etching by dilute HCl, dilute NH 4 OH, or buffer oxide etchant (BOE), the performance of Schottky diodes compared with samples without surface pre-treatment is improved significantly. Auger electron spectroscopy (AES) analysis of the thermally annealed Schottky diode has been performed to investigate the failure mechanism. No significant change was found for samples annealed up to 450°C. However, a drastic degradation of the barrier height and the ideality factor was observed in samples annealed at 500°C, which may be caused by the interdiffusion and penetration of metals into the semiconductor.

Quantum-confined Stark shift in electroreflectance of InAs/InxGa1−xAs self-assembled quantum dots

Electroreflectance was employed to study the electric-field effect on the interband transitions of InAs quantum dots embedded in an In0.16Ga0.84As matrix. The electric field caused an asymmetric quantum-confined Stark shift, which revealed a nonzero built-in dipole moment in the quantum dots. We found the ground-state and excited-state dipole moments to be in the same direction. The electron wave functions are distributed near the base of the quantum dot, with their centers located below the hole wave functions. We also observed a symmetric Stark shift in the wetting-layer transitions. This implies that the wetting-layer potential is symmetric, despite its being capped with quantum dots.

1.55μm emission from InAs quantum dots grown on GaAs

We report a comparative study on the growth of InAs quantum dots (QDs) on GaAs by metalorganic chemical vapor deposition using triethylgallium (TEGa) and trimethylgallium (TMGa) for the GaAs cap layer. QDs exhibit 1.3μm photoluminescence (PL) at room temperature, as the GaAs cap layer is directly grown on the QDs. The PL emission can be extended to 1.49μm when an In0.25Ga0.75As overgrown layer is inserted between the cap layer and the InAs QDs. The use of TMGa or TEGa for the growth of the GaAs cap layer is essential for a further increase in the emission wavelength of the InAs QDs. Strong PL emission at 1.55μm with a linewidth of 28meV can be obtained as the GaAs cap layer is grown by TEGa, while the optical properties degrade severely when using TMGa.

InAs/GaAs quantum dot lasers with InGaP cladding layer grown by solid-source molecular-beam epitaxy

This letter presents the lasing properties of InAs/GaAs quantum dot lasers with InGaP cladding layers grown by solid-source molecular-beam epitaxy. These Al-free lasers exhibit a threshold current density of 138 A/cm2, an internal loss of 1.35 cm−1, and an internal quantum efficiency of 31% at room temperature. At a low temperature, a very high characteristic temperature of 425 K and very low threshold current density of 30 A/cm2 are measured.

Energy spectrum of surface states of lattice-matched In0.52Al0.48As surface intrinsic-n+ structure

This work uses photoreflectance to investigate the band gap, built-in electric field, and surface Fermi level of a series of lattice-matched In0.52Al0.48As surface intrinsic-n+ structures having different undoped layer thickness. Experimental results indicate that the surface Fermi level is weakly pinned. By converting the dependence of the built-in electric field on undoped layer thickness into the dependence of surface state density on the surface Fermi level, this study defines the energy spectrum of the surface state density of InAlAs surface using a Gaussian distribution function.

Matrix-dependent structural and photoluminescence properties of In0.5Ga0.5As quantum dots grown by molecular beam epitaxy

Abstract The properties of the self-organized In 0.5 Ga 0.5 As quantum dots on In 0.1 Ga 0.9 As, GaAs, and In 0.1 Al 0.9 As surfaces and matrices are investigated using atomic force microscopy (AFM) and photoluminescence (PL). It is found that both the size variation and the density of the quantum dots depend closely on the matrix materials. PL spectra indicate that the In 0.5 Ga 0.5 As quantum dots in In 0.1 Ga 0.9 As matrix exhibit higher intensity as compared to those in GaAs and In 0.1 Al 0.9 As matrices. It is also found that the activation energy of the In 0.5 Ga 0.5 As quantum dots in GaAs matrix is higher than that of the dots in In 0.1 Ga 0.9 As matrix. Whereas the quantum dots in In 0.1 Al 0.9 As matrix exhibit the lowest activation energy due to higher carrier hopping probability and defect density.

Sb-based semiconductors for low power electronics

Sb-based semiconductors incorporating heterostructures of InP, InAs, AlSb, InSb, GaSb, InGaAs, InGaSb, GaAsSb and InGaAsSb can be used for high speed, low power applications such as wide-bandwidth telecommunications for aircraft, satellites, wireless communication, and global positioning systems, as well as thermophotovoltaic cells, THz medical imaging and remote sensing, IR sensors for space exploration, high resolution biomedical spectroscopy and military systems, including security scanners. Sb-based electronic devices such as heterojunction bipolar transistors (HBTs) offer high speed, low power consumption and good breakdown voltages. High electron mobility InAs/AlSb or InSb/AlSb and high hole mobility InGaSb/AlSb quantum well heterostructure field effect transistors (HFETs) have also been widely pursued for THz amplifiers and high speed complementary logic circuits.