Browsing by Author "Lee, HM"

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A low noise composite-channel metamorphic HEMT for wireless communication applications
(2003)
Lu, CY
;
Chen, KS
;
Lee, HM
;
Chang, EY
;
Chen, SH
A composite-channel Metamorphic high electron mobility transistor (MHEMT) was developed for low noise high linearity application. The MHEMT was grown by Molecular Beam Epitaxy (MBE) on GaAs substrates with InAlAs graded buffer. The composite-channel layers in the MHEMT include a top In0.55Ga0.45As layer, a middle In0.67Ga0.33As layer, and a bottom In0.55Ga0.45As layer. The design of this structure provides better electron confinement in the channel with less impact ionization as compared to conventional dual delta doped MHEMTs. This results in devices with higher linearity and drain to gate voltage as compared to the conventional metamorphic HEMTs. The 0.25x160 mum(2) device with the novel channel structure exhibits a maximum frequency of oscillation f(max) of 290 GHz and a current gain cut-off frequency f(t) of 110 GHz. The noise figure of the device at 6 GHz is 0.23 dB and the associated gain was 15.06 dB. The IP3 of the device at 6 GHz is 19.67 dBm. The composite channel metamorphic HEMT shows great potential for high linearity and low noise application at high frequencies.
A metamorphic high electron-mobitity transistor with reflowed submicron T-Gate for high-speed optoelectronics applications
(2003)
Lien, YC
;
Chang, EY
;
Chu, LX
;
Chang, HC
;
Lee, CS
A metamorphic high electron-mobility transistor (HEMT) manufactured with reflowed submicron T-gate using E-beam lithography for high-speed optoelectronics applications is developed. The In0.53Al0.47As/InGaAs HEMT uses InxAl1-xAs as the buffer layer between GaAs substrate and the InP lattice-matched HEMT structure. The T-gate developed has a gate length of 0.1 mum. The fabricated metamorphic HEMT has a saturation drain current of 280mA/mrn and a transconductance of 840mS/mm at V-DS=1.2V Noise figure for 160 mum gate-width device is less than 1 dB and the associated gain is up to 14dB at 18GHz. The device demonstrates a cut-off frequency f(T) of 150GHz and a maximum frequency f(MAX) up to 350GHz. The metamorphic HEMT developed has the potential for high-speed optoelectronics applications.
Composite-channel metamorphic high electron mobility transistor for low-noise and high-linearity applications
(2004-07-01)
Chang, EY
;
Lin, YC
;
Chen, GJ
;
Lee, HM
;
Huang, GW
A metamorphic high-electron-mobility transistor (MHEMT) with In0.55Ga0.45As/In0.67Ga0.33As/In0.55Ga0.45As composite channel layers was developed for low-noise and high-linearity applications. The use of: a composite channel results in high electron mobility and good confinement of electrons in the channel region which are the desired characteristics of low-noise and high-linearity devices. The noise figure of the 0.25 x 160 mum(2) devices is 0.23 dB with 15.06 dB associated gain, and the output third-order intercept point (IP3) is 18.67 dBm at 6 GHz. The device shows great potential for high-linearity and low-noise applications at high frequencies.
Controlled placement of self-organized Ge dots on patterned Si (001) surfaces
(2004-02-15)
Lee, HM
;
Yang, TH
;
Luo, GL
;
Chang, EY
;
材料科學與工程學系
The positioning and ordering of the self-organized Ge dots were controlled using the ultra high-vacuum chemical molecular epitaxial growth of Ge on electron beam lithographically patterned Si (001) substrates. The experimental results indicate that the edge smoothness of the etched Si holes affects the distribution and long-range ordering of the Ge dots formed. With optimized etching conditions, the Ge dots can be grown uniformly on the edges of the holes etched on the patterned Si substrates. The sizes of the Ge dots are approximately 10 nm. The proposed, technique can be applied to the fabrication of regimented arrays in signal processing applications.
Flower-like distributed self-organized Ge dots on patterned Si (001) substrates
(2003-06-15)
Lee, HM
;
Yang, TH
;
Luo, GL
;
Chang, EY
;
材料科學與工程學系
Self-organized Ge dots were obtained utilizing ultra high vacuum chemical molecular epitaxial growth of Ge on electron beam lithographically patterned Si (001) substrates. The dimensions of these etched Si mesa are 65/23/200 nm in diameter/height/period. The sizes and arrangement of the Ge dots were characterized by scanning electron microscopy and atomic force microscopy. The Ge dots have an average base width of 10 nm and the size is quite uniform. Due to the energetically favorable sites, the Ge dots tend to form homocentrically along the Si mesa edge, and their distribution is flower-like. [DOI: 10.1143/JJAP.42.L718].
InGaP/InGaAs PHEMT with high IP3 for low noise applications
(2004-06-10)
Lin, YC
;
Chang, EY
;
Chen, GJ
;
Lee, HM
;
Huang, GW
A low noise InGaP/InGaAs pseudomorphic high-electron-mobility transistor (PHEMT) with high IN was developed. The device utilises InGaP as the Schottky layer to achieve a low noise figure and uses AlGaAs as the spacer to reform the electron mobility and contains dual delta doped layers to improve the device linearity.
Low-noise metamorphic HEMTs with reflowed 0.1 mu m T-gate
(2004-06-01)
Lien, YC
;
Chang, EY
;
Chang, HC
;
Chu, LH
;
Huang, GW
A 0.1-mum T-gate fabricated using e-beam lithography and thermally reflow process was developed and applied to the manufacture of the low-noise metamorphic high electron-mobility transistors (MHEMTs). The T-gate developed using the thermally reflowed e-beam resist technique had a gate length of 0.1 mum and compatible with the MHEMT fabrication process. The MHEMT manufactured demonstrates a cutoff frequency f(T) of 154 GHz and a maximum frequency f(max). of 300 GHz. The noise figure for the 160 mum gate-width device is less than 1 dB and the associated gain is up to 14 dB at 18 GHz. This is the first report of a 0.1 mum MHEMT device manufactured using the reflowed e-beam resist process for T-gate formation.
Molecular beam epitaxial growth and photoluminescence studies of InAs self-organized quantum dots on patterned GaAs (001) substrates
(2001)
Lee, BC
;
Lee, HM
;
Wu, JC
;
Chang, YP
;
Sun, KW
We present experimental results on the growth of InAs self-organized quantum dots on patterned substrates via molecular beam epitaxy. Luminescence spectra of these quantum dots have been studied.
New nanometer T-gate fabricated by thermally reflowed resist technique
(2002-12-15)
Lee, HM
;
Chang, EY
;
Chen, SH
;
Chang, CY
;
電子工程學系及電子研究所
Novel nanometer T-gate process has been developed utilizing electron beam (EB) lithography and thermally reflowed resist technique. Through well-controlled EB exposure dosage, heating time and reflow temperature; the resist structures can be efficiently reflowed to form the desired T-gate configuration with dimension ranging from 150 nm to 30 nm. After Ti/Pt/Au metal deposition by electron gun evaporation and lift-off process, the nanometer T-gates with thickness of about 500 nm were formed. With the optimized conditions, ultra-short 30 nm T-shaped gate was clearly demonstrated on the GaAs substrate. This is the smallest T-gate reported with the thermally reflowed technique in the literature so far and can practically be used in the GaAs monolithic microwave integrated circuit (MMIC) fabrications.
Selective growth of single InAs quantum dots using strain engineering
(2002-01-14)
Lee, BC
;
Lin, SD
;
Lee, CP
;
Lee, HM
;
Wu, JC
A method to achieve ordering and selective positioning of single InAs self-assembled quantum dots (QDs) has been developed. The selective growth was achieved by manipulating the strain distribution on the sample surface. The QDs are formed on predesigned mesas with added strain. Single dots were obtained on small mesas. Using this technique, two-dimensional single QD arrays have been achieved. (C) 2002 American Institute of Physics.
Use WNx as diffusion barrier for copper airbridged low noise GaAsPHEMT
(2003-11-27)
Chang, HC
;
Chang, EY
;
Lien, YC
;
Chu, LH
;
Chang, SW
A low noise pseudomorphic high electron mobility transistor (PHEMT) with copper airbridges using sputtered WNx as the diffusion barrier has been developed. Both the material system and the copper airbridged PHEMT with WNx as the diffusion barrier did not decay even after thermal annealing at 250degreesC for 20 h. The results show that the copper airbridges with WNx diffusion barrier can be used as the interconnects for low noise GaAs PHEMTs.