Seong-June Jo

Reduction of dark current in an n-type In0.3Ga0.7As/GaAs quantum well infrared photodetector by using a camel diode structure

Abstract Long wavelength infrared absorption characteristics of an In0.3Ga0.7As/GaAs quantum well infrared photodetector (QWIP) employing an n-i-p-i-n camel diode structure were compared with those of a conventional n-QWIP. The QWIPs showed a photocurrent response peak at the wavelength of approximately 10 μm due to electronic intersubband transitions in quantum wells. The QWIP employing the camel diode structure showed a reduced dark current, an increased responsivity, and thus an improved detectivity compared with those of the conventional n-QWIP due to the presence of the n-i-p-i-n camel barrier. The results indicated the potential of the QWIP employing an n-i-p-i-n camel diode structure for use in infrared detectors operating at elevated operating temperature.

Molecular beam epitaxy growth and characterization of InGaP/InGaAs pseudomorphic high electron mobility transistors (HEMTs) having a channel layer over critical layer thickness

In/sub 0.5/Ga/sub 0.5/P/In/sub x/Ga/sub 1-x/As (x=0.33 and 0.40), pseudomorphic high electron mobility transistors (p-HEMTs) having a channel layer over the critical layer thickness were grown on patterned and nonpatterned GaAs substrates by using a compound-source molecular beam epitaxy (MBE). Characteristics of the highly strained InGaP/In/sub x/Ga/sub 1-x/As (x=0.33 and 0.40) p-HEMTs grown on patterned substrates were compared with those of conventional InGaP/In/sub 0.22/Ga/sub 0.78/As p-HEMTs grown on a nonpatterned substrate. The highly strained InGaP/In/sub 0.33/Ga/sub 0.67/As p-HEMT showed substantial improvements in device performances including DC (drain saturation current and transconductance), microwave (f/sub T/ and f/sub max/), low-frequency noise (Hooge parameter), and high-frequency noise (minimum noise figure and associated gain) characteristics compared with those of the conventional InGaP/In/sub 0.22/Ga/sub 0.78/As p-HEMT. The improvements in device performances of the highly strained InGaP/In/sub 0.33/Ga/sub 0.67/As p-HEMT are attributed to the improved transport property of the high-quality highly strained In/sub 0.33/Ga/sub 0.67/As channel layer achieved by the use of the patterned substrate growth. The results indicate the potential of highly strained InGaP/In/sub x/Ga/sub 1-x/As p-HEMTs having a channel layer in excess of the critical layer thickness grown on patterned GaAs substrates for use in high-performance microwave device applications.

Effects of rapid thermal annealing on quality of In0.52Al0.48As∕In0.53Ga0.47As multiquantum wells grown on a compositionally graded InAlAs∕InAlGaAs metamorphic buffer layer

We report improvement in crystalline quality of In0.52Al0.48As∕In0.53Ga0.47As multiquantum wells (MQWs) and compositionally graded InAlAs∕InAlGaAs metamorphic buffer grown on GaAs by using postgrowth rapid thermal annealing (RTA). Dependence of optical and structural properties of the MQWs on RTA was investigated by using photoluminescence (PL) and triple-axis x-ray diffraction measurements. After the RTA, the PL intensity of the MQWs increased, while the linewidth decreased. Also, the triple-axis contour maps of the MQWs showed increase in peak intensity of epilayers as well as crystalline reformation indicated by narrower mosaic spread and restoration of epilayer tilt to the substrate orientation.

In0.5Ga0.5P/In0.22Ga0.78As pseudomorphic high electron mobility transistors with an oxidized GaAs gate for improved breakdown voltage characteristics

DC and RF characteristics of In0.5Ga0.5P/In0.22Ga0.78As pseudomorphic high electron mobility transistors (p-HEMTs) having a gate oxide layer were investigated. 1.5×50μm2 gate p-HEMTs having the gate oxide thickness of 0, 50, and 300 A were fabricated by using a liquid phase oxidation technique of GaAs. Substantial improvements in gate leakage current and on-state and off-state breakdown voltage characteristics of p-HEMTs having a gate oxide layer were observed. The on-state breakdown voltage (∼13.2 V) of the p-HEMTs having a 50 A gate oxide layer was ≈2.3 times lager than that of the p-HEMTs without a gate oxide layer. While the p-HEMTs having a gate oxide layer of 300 A showed much improved gate leakage current and on-state breakdown voltage characteristics, they suffered from degradation of output conductance due to the drain induced barrier lowering originating from the thick gate oxide layer. While optimization of p-HEMT epitaxial layer structure for metal-oxide-semiconductor gate operation is required for further improvements in device characteristics, the preliminary results indicate the potential of In0.5Ga0.5P/In0.22Ga0.78As/GaAs p-HEMT having a gate oxide layer for high power applications.

Effects of postgrowth rapid thermal annealing on InAlAs∕InGaAs metamorphic high-electron-mobility transistor grown on a compositionally graded InAlAs∕InGaAlAs buffer

Effects of postgrowth rapid thermal annealing (RTA) on structural and electrical properties of an In0.52Al0.48As∕In0.52Ga0.48As metamorphic high-electron-mobility transistor (MHEMT) structure grown on a GaAs substrate utilizing a compositionally graded InAlAs∕InGaAlAs buffer layer were investigated. High-resolution triple-axis x-ray diffraction, photoluminescence, and van der Pauw–Hall measurements were used for the investigation. While the RTA improved the structural property of the MHEMT, it degraded the channel mobility of the MHEMT due to defect-assisted impurity redistribution.

Crystalline quality improvement of In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As heterostructure on InAlAs/InGaAlAs/GaAs metamorphic buffer by post-growth rapid thermal annealing

Effects of post-growth rapid thermal annealing (RTA) on optical and structural properties of an In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As multi-quantum-well (MQW) structure on a GaAs substrate by using an InAlAs/InGaAlAs metamorphic buffer were investigated. Photoluminescence spectrum and triple-axis (004) contour maps showed improvement in crystalline quality of the metamorphic MQW structure through the post-growth RTA.

The application of a passive mode-locked fiber laser including NALM to electro-optic sampling

We constructed an electro-optic sampling (EOS) system using a passive mode-locked fiber laser including nonlinear amplifier loop mirror (NALM). We used an optical band-pass filter and a polarization dependent isolator to get a pure single soliton pulse having the stable polarization state. The pulse width and the repetition rate were about 600 fs and 2 MHz respectively. We could achieve the impulse response measurement of the Schottky-type InGaAs photodetector (PD) using EOS system utilizing this fiber laser.

Investigation of strain effects on performance of high-speed Schottky-type photodetectors

PIN and Schottky photodetectors (PDs) having an InGaAs absorption layer are widely used for long distance optical communication. The speed of those PDs is generally limited by hole transition time in the absorption layer. This limit can be overcome by using a tensile-strain In/sub x/Ga/sub 1-x/As (x<0.53) absorption layer. We fabricated and characterized Schottky-type PDs having a lattice-matched In/sub 0.53/Ga/sub 0.47/As absorption layer and a tensile-strained In/sub 0.48/Ga/sub 0.52/As absorption layer. Photocurrent impulse response of the tensile-strained InAlAs/In/sub 0.48/Ga/sub 0.52/As PD showed an improved FWHM of 13 ps, while that of the the lattice-matched InAlAs/In/sub 0.53/Ga/sub 0.47/As PD was 16 ps.

InP-based MOSFET technology utilizing a liquid phase oxidized InGaAs gate

We first report the characteristics of InGaAs-oxide grown by a liquid phase oxidation using a gallium-ion-contained nitric acid solution and an oxygen plasma treatment and depletion-mode In/sub 0.53/Ga/sub 0.47/As- and InP-channel MOSFETs using the InGaAs-oxide. The characteristics of InGaAs-oxide showed low leakage current and small capacitance-voltage hysteresis. 1.5/spl times/50 /spl mu/m/sup 2/ depletion-mode In/sub 0.53/Ga/sub 0.47/Asand InP-channel MOSFETs were fabricated by using a conventional optical lithography. The gate oxide was formed by a liquid phase oxidation of InGaAs ohmic cap layer and subsequently an oxygen plasma treatment after mesa etching and ohmic metallization. The drain current-voltage characteristics of In/sub 0.53/Ga/sub 0.47/As- and InP-channel MOSFETs showed a complete pinch-off and saturation. The f/sub T/ and f/sub max/ of the In/sub 0.53/Ga/sub 0.47/As-channel MOSFET were approximately 9 GHz and 10 GHz, respectively, and those of the InP-channel MOSFET were approximately 10.5 GHz and 70 GHz, respectively.

Improved speed performance of tensile-strained In/sub x/Ga/sub 1-x/As (x<0.53) photodetectors utilizing a patterned substrate growth

Photodetectors (PDs) play an important role in optical communication systems and measurement systems. As the bandwidth of the optical communication system is increasing rapidly, high-speed PDs are needed. The mesa-type PDs such as Schottky and PIN-type PDs having InGaAs absorption layers are generally used for that field. The speed of those PDs in general is limited by hole transition time in the absorption layer. The speed performance limitation of mesa-type PDs due to the hole transition time can be improved by using a tensile-strained In/sub x/Ga/sub 1-x/As (x<0.53) absorption layer. It was shown by simulations that the effective hole mass could be reduced by utilizing a tensile-strained In/sub x/Ga/sub 1-x/As (x<0.53) absorption layer. Tensile-strained InAlAs/In/sub 0.48/Ga/sub 0.52/As and lattice-matched InAlAs/In/sub 0.53/Ga/sub 0.47/AS Schottky-type PDs were fabricated and characterized. Impulse response (FWHM) of the tensile-strained PD was reduced to 13 ps as compared with that (16 ps) of the lattice-matched PD, which is attributed to the improved hole transport property in the tensile-strained In/sub 0.48/Ga/sub 0.52/As absorption layer.