Changhyun Yi

Effect of donor-complex-defect-induced dipole field on InAs/GaAs quantum dot infrared photodetector activation energy

In order to understand dopant incorporation in quantum dot infrared photodetectors, three quantum dot (QD) Schottky diodes (undoped, delta doped, and modulation doped) have been investigated. Donor-complex-defect (DX) centers have been observed by photocapacitance quenching in the doped diodes only. When the applied bias increases, the doped samples show a rapid increase in dark current and a resulting dramatic decrease in QD activation energy. The activation energy reduction could be related to a dipole field between positively charged DX centers and electrons in QDs. A transport mechanism is proposed to explain the observed activation energy bias dependence in the doped samples.

Interfacial reactions during GaN and AiN epitaxy on 4H– and 6H–SiC(0001)

Thin layers of AlN and GaN have been grown by plasma-assisted molecular beam epitaxy on Si-face 4H– and 6H–SiC(0001)Si substrates. The impact of the SiC surface preparation and oxide removal via a Ga deposition and desorption process on the chemistry and structure of the GaN/SiC and AlN/SiC interfaces, and on the GaN/SiC subsurface reactivity is characterized. We also investigate the impact of this process on growth mode evolution.

Doping characterization of InAs/GaAs quantum dot heterostructure by cross-sectional scanning capacitance microscopy

Cross-section of multi-layer InAs/GaAs quantum dot heterostructure has been characterized using scanning capacitance microscopy to investigate dopant incorporation into quantum dots. Simulation of the corresponding band structure is used to better understand the experimental results.

Band discontinuity measurements of the wafer bonded InGaAs∕Si heterojunction

p-type InGaAs∕Si heterojunctions were fabricated through a wafer fusion bonding process. The relative band alignment between the two materials at the heterointerface was determined using current-voltage (I-V) measurements and applying thermionic emission-diffusion theory. The valence and conduction band discontinuities for the InGaAs∕Si interface were determined to be 0.48 and −0.1eV, respectively, indicating a type-II band alignment.

DX-like centers in InAs∕GaAs QDIPs observed by polarization-dependent Fourier transform infrared spectroscopy

In order to decrease dark current density and improve spectral response tunability of quantum dot infrared photodetectors (QDIPs), it is critical to understand how dopants are incorporated into quantum dot active regions. In this article, polarization-dependent Fourier transform infrared absorbance spectroscopy is used to measure intraband absorption in InAs∕GaAs QDIP heterostructures featuring different molecular beam epitaxy remote doping schemes. In addition to a QD absorbance peak near 90meV, a peak at 405meV is observed. This peak at 405meV demonstrates signature characteristics of DX centers in III-V semiconductors, such as spherical symmetry, thermal activation of trapped carriers with increasing temperature, and dependence of absorbance peak magnitude (and thereby DX center concentration) on doping concentration and doping scheme. A conduction band energy diagram for the observed DX-like center and the corresponding optical ionization process is proposed. In addition, the effect of these DX-like c...

Impact of arsenic species (As2∕As4) on the relaxation and morphology of step-graded InAsxP1−x on InP substrates

The influence of arsenic species (As2 or As4) on compositionally graded InAsxP1−x buffer layers (x=0.15–0.8) grown by molecular beam epitaxy on InP is investigated. It was found that As2 has a higher incorporation rate than As4. Anisotropic strain relaxation occurs for samples grown with As4, with higher relaxation along [110] and lower relaxation along [1–10]. Relatively high and isotropic strain relaxation occurs for buffers grown with As2. The observed mosaic broadening is much greater when using As2. Atomic force microscopy morphological features are consistent with the strain relaxation results. Strong corrugations along [1–10] dominate the surface of films grown with As4, while grainy surfaces occur with As2. The use of As4 increased the overall surface roughness. The authors interpret these results with a simple model: the higher incorporation rate of As2 enables In to incorporate more uniformly in the two perpendicular ⟨110⟩ directions, while the lower incorporation rate of As4 decreases this unif...

Impact of unintentional and intentional nitridation of the 6H-SiC(0001)Si substrate on GaN epitaxy

We report the impact of both unintentional and intentional nitridation of 6H-SiC(0001)Si substrates on the epitaxial growth of GaN by molecular-beam epitaxy. The unintentional nitridation is dependent upon the details of the pregrowth Ga flash-off process used to remove surface oxides and to achieve a specific pregrowth surface reconstruction. The nucleation process and structural and morphological properties of GaN epitaxial layers are strongly influenced by the modifications of the SiC surface induced by the pregrowth preparation process. We found that residual oxygen at the SiC surface, unintentional SiC nitridation, and the formation of cubic GaN grains at the initial nucleation stage strongly decrease as the concentration of Ga used is increased during the flash cleaning. In addition, recent work has shown that the use of a SiN interlayer for GaN epitaxy on various substrates reduces dislocation density. We observe an improvement in the heteroepitaxy of GaN when the SiC surface is intentionally nitri...

Neural network based modeling of diffusion process for high-speed avalanche photodiodes fabrication

Abstract This paper presents the modeling methodology of Zn diffusion process utilized for high-speed avalanche photodiode fabrication using neural networks. The modeling scheme can characterize the effects of diffusion process conditions on the performance metrics of diffusion process. Three different InP-based test structures with different doping concentrations in diffused layer are explored. Three input factors (sealing pressure, amount of Zn 3 P 2 source per volume, and doping concentration of diffused layer) are examined with respect to the two performance metrics (diffusion-rate and Zn doping concentration) by means of D-optimal design experiment. Diffusion rate and Zn doping concentration in diffused layer are characterized by a response model generated by training feed-forward error back-propagation neural networks. It is observed that the neural network based process models developed here exhibit good agreement with experimental results.

Control of dopant incorporation in InAs/GaAs quantum dots for infrared photodetection with low dark current

To reduce dark current in quantum-dot infrared photodetectors, different InAs/GaAs quantum-dot doping conditions, i.e. concentration and modulation- vs. delta-doping, have been investigated by the comparison of temperature-dependent dark current and corresponding activation energies vs. bias.

Doping Characterization of InAs/GaAs Quantum Dot Heterostructure by Cross-Sectional Scanning Capacitance Microscopy

Cross-section of multi-layer InAs/GaAs quantum dot heterostructure has been characterized using scanning capacitance microscopy to investigate dopant incorporation into quantum dots. Simulation of the corresponding band structure is used to better understand the experimental results.