• Korean Journal of Materials Research
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• v.14 no.2
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• pp.146-151
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• 2004

We investigated the effects of high potential barriers on the optical characteristics of InAs quantum dots (QDs) by using photoluminescence (PL) and photoreflectance (PR) spectroscopy. A sample with regular InAs quantum dots on GaAs was grown by molecular beam epitaxy (MBE) as a reference. Another InAs QDs sample was embedded in single AlGaAs barriers. On the other hand, a sample with GaAs/AlGaAs superlattice barriers was adopted for comparison with a sample with a single AlGaAs layer. In results, we found that the emission wavelength of QDs was effectively tailored by using high potential barriers. Also, it was found that the optical properties of a sample with QDs embedded in GaAs/AlGaAs superlattices were better than those of a sample with QDs embedded in a single layer of AlGaAs barriers. We believe that GaAs/AlGaAs superlattice could effectively prevent the generation of defects.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.391-392
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• 2012

In these days, the desire for the precise and tiny displays in mobile application has been increased strongly. Currently, laser displays ranging from large-size laser TV to mobile projectors, are commercially available or due to appear on the market [1]. In order to achieve a mobile projectors, the semiconductor laser diodes should be used as a laser source due to their size and weight. In this presentation, the continuous etch characteristics of Pd and AlGaN/GaN superlattice for the fabrication of blue laser diodes were investigated by using inductively coupled $CHF_3$ and $Cl_2$ -based plasma. The GaN laser diode samples were grown on the sapphire (0001) substrate using a metal organic chemical vapor deposition system. A Si-doped GaN layer was grown on the substrate, followed by growth of LD structures, including the active layers of InGaN/GaN quantum well and barriers layer, as shown in other literature [2], and the palladium was used as a p-type ohmic contact metal. The etch rate of AlGaN/GaN superlattice (2.5/2.5 nm for 100 periods) and n-GaN by using $Cl_2$ (90%)/Ar (10%) and $Cl_2$ (50%)/$CHF_3$ (50%) plasma chemistry, respectively. While when the $Cl_2$/Ar plasma were used, the etch rate of AlGaN/GaN superlattice shows a similar etch rate as that of n-GaN, the $Cl_2/CHF_3$ plasma shows decreased etch rate, compared with that of $Cl_2$/Ar plasma, especially for AlGaN/GaN superlattice. Furthermore, it was also found that the Pd which is deposited on top of the superlattice couldn't be etched with $Cl_2$/Ar plasma. It was indicating that the etching step should be separated into 2 steps for the Pd etching and the superlattice etching, respectively. The etched surface of stacked Pd/superlattice as a result of 2-step etching process including Pd etching ($Cl_2/CHF_3$) and SLs ($Cl_2$/Ar) etching, respectively. EDX results shows that the etched surface is a GaN waveguide free from the Al, indicating the SLs were fully removed by etching. Furthermore, the optical and electrical properties will be also investigated in this presentation. In summary, Pd/AlGaN/GaN SLs were successfully etched exploiting noble 2-step etching processes.

• KIEE International Transactions on Electrophysics and Applications
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• v.2C no.5
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• pp.258-261
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• 2002

Electrical forming dependent current-voltage (I-V) and numerically derived differential conductance(dI／dV) characteristics have been presented in the multi-layer nano-crystalline silicon／oxygen (no-Si／O) superlattice. Distinct staircase-like features, indicating the presence of resonant tunnel barriers, are clearly observed in the dc I-V characteristics. Also, all samples showed a continuous change in current and zero conductivity around OV corresponding to the Coulomb blockade in the calculated dI／dV-V curve. Also, Ra-man scattering measurement showed the presence of a nano-crystalline Si structure. This result becomes a step in the right direction for the fabrication of silicon-based optoelectronic and quantum devices as well as for the replacement of silicon-on-insulator (SOI) in high speed and low power silicon MOSFET devices of the future.

• Proceedings of the Korean Vacuum Society Conference
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• 2003.08a
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• pp.128-128
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• 2003

• Journal of the Korean Vacuum Society
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• v.22 no.6
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• pp.321-326
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• 2013

The effect of rapid thermal annealing (RTA) on the optical properties of digital-alloy InGaAlAs multiple quantum well (MQW) structures have been investigated by using photoluminescence (PL) and time-resolved PL measurements as a function of RTA temperature. The MQW samples were annealed from $700^{\circ}C$ to $850^{\circ}C$ for 30 s in a nitrogen atmosphere. The MQW sample annealed at $750^{\circ}C$ exhibited the strongest PL intensity and the narrowest FWHM (Full width at half maximum), indicating the reduced nonradiative recombination centers and the improved interfaces between the wells and barriers. The MQW samples annealed at $800^{\circ}C$ and $850^{\circ}C$ showed the decreased PL intensities and blueshifted PL peaks compared to $750^{\circ}C$-annealed sample. The blueshift of PL peak with increasing RTA temperatures are ascribed to the increase of aluminum due to intermixing of gallium (Ga) and aluminum (Al) in the interfaces of InGaAs/InAlAs short-period superlattices. The decrease of PL intensity after annealing at $800^{\circ}C$ and $850^{\circ}C$ are attributed to the interface roughening and lateral composition modulation caused by the interdiffusion of Ga and Al and indium segregation, respectively. With increasing RTA temperature the PL decay becomes slower, indicating the decrease of nonradiative defect centers. The optical properties of digital-alloy InGaAlAs MQW structures can be improved significantly with optimum RTA conditions.