Jae-Min Jang

Fabrication and characterization of self-assembled InGaN quantum dots by periodic interrupted growth

Self-assembled InGaN quantum dots are fabricated in a two-flow horizontal MOCVD reactor maintained at the pressure of 200torr. The precursors were trimethyl-gallium (TMG) and trimethyl-indium (TMI) and ammonia (NH3), and the carrier gas was N2 and H2. The optimum condition was deduced to fabricate the InGaN quantum dots. GaN nucleation layer was grown at 500°C with thickness of 25nm, and then 2~3 μm thick GaN buffer-layer was deposited at 1050 °C. InGaN quantum dots were grown on GaN buffer layer. Carrier gas was changed with N2 instead of H2 in QD growth. In the growth of InGaN quantum dots, NH3 was supplied in cyclic periodic interrupted mode with the interval of 5 seconds. The influence of number of periodic interrupted NH3 on the structural and optical properties of InGaN quantum dots was investigated by AFM, FE-SEM and photoluminescence (PL). The InGaN quantum dots are grown by 2 periods growth and have 0.4nm in height and 31nm lateral size. The height of quantum dots was increased with increase of growth periods, and the lateral size was decreased after 3 periods and then increased in 4 periods. The density of InGaN quantum dots with 3 periods and 4 periods was measured to be 1.51×1011/cm2 and 8.91×1010/cm2. Density of InGaN quantum dots was decreased after 3 periods, and this is attributed to the coalescence. A strong peak at 362.2 nm (3.41eV) and broad emission peak in 532.9~663.9nm (2.33~1.86eV) were evolved in the photoluminescence measurement using Nd-YAG laser with wavelength of 266nm. Addition emission peak was found in the range 433.7nm~462.2nm (2.85eV~2.68eV) in the samples with 3 periods and 4 periods interruption, and this peak was identified as the InGaN quantum dots with low indium concentration.

유기금속기상증착법에 의한 InGaN/GaN 양자점 구조의 성장거동

Growth behavior of InGaN/GaN self-assembled quantum dots (QDs) was investigated with respect to different growth parameters in low pressure metalorganic chemical vapor deposition. Locally formed examples of three dimensional InGaN islands were confirmed from the surface observation image with increasing indium source ratio and growth time. The InGaN/GaN QDs were formed in Stranski-Krastanow (SK) growth mode by the continuous supply of metalorganic (MO) sources, whereas they were formed in the Volmer-Weber (V-W) growth mode by the periodic interruption of the MO sources. High density InGaN QDs with 1~2nm height and 40~50nm diameter were formed by the S-K growth mode. Dome shape InGaN dots with 200~400nm diameter were formed by the V-W growth mode. InN content in InGaN QDs was estimated to be reduced with the increase of growth temperature. A strong peak between 420-460 nm (2.96-2.70 eV) was observed for the InGaN QDs grown by S-K growth mode in photoluminescence spectrum together with the GaN buffer layer peak at 362.2 nm (3.41 eV).

Properties of aluminum doped zinc oxide thin film by sol-gel process

The thin films of transparent conductive aluminum doped ZnO have been deposited by the sol-gel process. In this study, important deposition parameters were thoroughly investigated in order to find appropriate procedures to grow large area thin films of low resistivity and high transparency at low cost for device applications. Experimental results indicated that the annealing temperature affected the crystal structure of the aluminum doped ZnO films considerably, but the controlling of effective doping concentration was the key point to achieve low film resistance by sol-gel process. It was adjusted by controlling the precursor concentration. Although the structure of our aluminum doped ZnO films did not have the preferred orientation along (002) plane, they had a high transmittance of over 87 % in visible region. In our experiments, the most suitable Al doped concentration was 1~4 mol%. The annealing temperature for the pre-heat treatment was 250 °C and post-heat treatment was 400-600 °C. The Al doped and undoped ZnO films are very uniform and compact. It is confirmed that the doping concentration and thermal treatment are important factor with electrical conductivity of ZnO films.

Fabrication of InGaN quantum dots by periodically interrupted growth in MOCVD

Self-assembled InGaN quantum dots are fabricated in a two-flow horizontal MOCVD reactor maintained at the pressure of 200 torr. The precursors were trimethyl-gallium (TMG) and trimethyl-indium (TMI) and ammonia (NH3), and the carrier gas was N2 and H2. The optimum condition for periodically interrupted growth (PIG) mode was deduced to fabricate the InGaN quantum dots. NH3 was supplied in PIG mode with the interval of 3 seconds and 5 seconds while TMG and TMI were supplied continuously. The carrier gas was N2 in QDs growth, while H2 in nucleation and buffer layer growth. The influence of number of periodic interrupted NH3 on the structural and optical properties of InGaN quantum dots was investigated by AFM, FE-SEM and low temperature photoluminescence (LT-PL). The AFM images give the size of InGaN QDs with diameter of 20 ~ 50 nm, height of 3 ~ 10 nm and density of 1010 #/cm2 ~ 1011 #/cm2. A strong peak at 362.2 nm (3.41eV) and broad emission peak in 435 nm (2.86 eV) were evolved in the photoluminescence measurement using Nd-YAG laser. The composition of QDs was estimated to be In0.14Ga0.86N from the relation between peak energy and indium content. Hence. The periodic interruption growth enables the fabrication of self- assembled InGaN QDs with high density and uniform size.

Patterned growth of ZnO nanorod by solution chemical method

A simple method has been developed for the controlled patterned growth of the ZnO nanorod arrays with different size and shape on substrate. In order to control the position of the ZnO nanorods, exposed ZnO seed is defined, as orderly aligned arrays, with the assistance of photolithography. This technique hinges on the patterning of the seed layer comprised by ZnO sol-gel precursor. The simple way to create patterned ZnO seed array is to use negative photoresist for ZnO seed coating. The UV exposures were performed though mask patterned various shape. The ZnO arrays are synthesized using solution chemical method at normal atmospheric pressure without any metal catalyst. A simple two-step process is developed for ZnO nanorod on substrate at 90°C. The ZnO seed precutsor is prepared by sol-gel process. The ZnO nanorod is grown by solution chemical method. The ZnO nanorod growth was dependent on the ZnO seed layer. The ZnO nanorods have length of 400~500nm and diameter of 25~50nm. The ZnO nanorod is single crystals with wurtzite and grows along the c axis of the crystal plane. The room temperature photoluminescence measurements have shown ultraviolet peaks 378.3nm (3.27eV) with high intensity.

Fabrication of well-aligned ZnO nanorods by hydrothermal process using GaN epitaxial layer

One dimensional (1-D) ZnO nanorod structure of hexagonal shape was fabricated on epitaxial GaN layer by hydrothermal method. The growth of GaN epitaxial layer was carried out in a two-flow horizontal MOCVD reactor maintained at a pressure of 200 torr. Firstly, a 25 nm thick GaN buffer layer was grown at 520 °C. Then 2~3&mgr;m thick GaN epilayer was deposited at 1070 °C. Trimethylgallium (TMG) and NH3 were used as Ga and N source, and H2 gas was used as carrier gas. After the deposition of GaN epilayer thin-film, single crystalline ZnO nanorod was fabricated in aqueous solution. XRD and FE-SEM results showed ZnO nanorod arrays were oriented highly along the (002) plane. The ZnO nanorod was analyzed to have good quality crystallization by FE-TEM. The SAED pattern has shown that ZnO nanorod was grown in the direction along (002)-plane. Photoluminescence (PL) has shown that the GaN-ZnO hetero-structure has shown ultra-violet lasing action at room temperature. Narrow and strong ultra-violet peak was observed in comparison with PL result from epitaxial GaN layer. The analysis results have proved that aqueous solution growth method developed in the present work can be a good application for optical electronic device.

Formation of InGaN self-assembled quantum dots on GaN by metal-organic chemical vapor deposition with NH3 periodic interruption growth

Self-assembled InGaN QDs on GaN epi-layer were grown by metal-organic chemical vapor deposition. In the growth of InGaN QDs, NH3 was supplied in cyclic interrupted mode with interval of 3 seconds and 5 seconds. This work enables the fabrication of dense, uniform InGaN QDs, and is potentially applied to optical materials systems.