Yi-Jen Chan

High-performance evanescently edge coupled photodiodes with partially p-doped photoabsorption layer at 1.55-/spl mu/m wavelength

In this letter, we demonstrate a high-performance evanescently coupled photodiode (ECPD) with the partially p-doped photoabsorption layer. As compared to the control ECPD with the traditional intrinsic photoabsorption layer, the demonstrated device can exhibit much higher output saturation current (power) and electrical bandwidth without sacrificing the quantum efficiency performance. By properly designing the geometry size and epilayer structures of the partially p-doped ECPD, very high responsivity (1.01 A/W), high electrical bandwidth (around 50 GHz), and high saturation current bandwidth product (920 mA/spl middot/GHz, at 40 GHz) have been achieved simultaneously at 1.55-/spl mu/m wavelength.

High-responsivity InGaAs MSM photodetectors with semi-transparent Schottky contacts

High-performance metal-semiconductor-metal photodetectors (MSM-PDs) with interdigitated semi-transparent Au Schottky contacts have been fabricated on pseudomorphic In/sub 0.9/Ga/sub 0.1/P-InP-InGaAs heterostructure. The responsivity measured at 1.55-/spl mu/m wavelength is greatly enhanced from 0.4 A/W to 0.7 A/W as the thickness of the Au electrodes is decreased to 10 nm. This corresponds to a 75% improvement over the conventional MSM-PDs with opaque metal electrodes. With a pseudomorphic InGaP barrier-enhancement layer, these devices exhibit a dark current density as low as 1.6 pA//spl mu/m/sup 2/. Extremely linear photoresponse without any internal gain is also observed for these detectors. The full-width at half maximum of the temporal response for the devices with semi-transparent electrodes is about 85 ps compared to 80 ps for the conventional ones. >

High-performance large-area InGaAs MSM photodetectors with a pseudomorphic InGaP cap layer

We report the fabrication and characteristics of high-performance InGaAs MSM photodetectors with a 300-/spl mu/m/spl times/300-/spl mu/m square and a 300-/spl mu/m-diameter circular detection area. With a pseudomorphic In/sub 0.9/Ga/sub 0.1/P cap layer, the detectors exhibit dark current densities less than 1 pA//spl mu/ on finger spacing. Bandwidth over 1 GHz has been obtained for these large-area detectors. Our results also show that the circular detector exhibits better speed performance as compared to the square one due to its smaller parasitic RC constant. >

Selectively dry-etched n+-GaAs/AlGaAs/n-InGaAs doped-channel FETs by using a CHF3+BCl3 plasma

Abstract The gate recess, which involves removing the n+-cap layer before putting the Schottky gate, is the most critical procedure in the fabrication of heterostructure field effect transistors (HFETs). Excellent etching depth control is required in order to obtain a uniform threshold voltage distribution, which is essential for high performance integrated circuit fabrication. A newly developed high selective reactive ion etching (RIE) based on CHF3+BCl3 plasma has been studied for the gate-recess-technique in GaAs/AlGaAs heterostructure FETs, where the non-volatile AlF3 compound is found to prevent the further etching in AlGaAs films. By changing the mixing ratio between chlorine- (BCl3) and fluorine-based (CHF3) gases, an etching selectivity of about 40 between the GaAs and AlGaAs materials was obtained. Using this optimum condition for later gate recessing, we have successfully fabricated the AlGaAs/InGaAs/GaAs heterostructure doped-channel FET. Device characteristics and the RIE associated damages have also been evaluated.

Characteristics of pseudomorphic AlGaAs/InxGa1−xAs (0≤x≤0.25) doped‐channel field‐effect transistors

The pseudomorphic properties of doped‐channel field‐effect transistors have been thoroughly investigated based on AlGaAs/InxGa1−xAs (0≤x≤0.25) heterostructures with different In contents. Through various analytical schemes and device characterization, we observed that by introducing a 150 A strained In0.15Ga0.85As channel we can enhance device performance; however, this strained channel is not stable after high‐temperature heat treatment. By further increasing the In content up to x=0.25, the device performance started to degrade, which is associated with strain relaxation in this highly strained channel.

The Monolithic Integration of a Wavelength-Demultiplexer With Evanescently Coupled Uni-Traveling-Carrier Photodiodes

In this letter, we discuss a novel integration of a wavelength demultiplexer with a pair of uni-traveling-carrier photodiodes (UTC-PDs). With this integrated module, we could separate incoming wavelengths of 1530 and 1550 nm, which are near the wavelengths utilized for digital and analog signal transmission in coarse wavelength-division multiplexing (CWDM) systems. The integrated UTC-PDs exhibited the following advantages: a wide 3-dB bandwidth (25 GHz), a reasonable responsivity (0.35 A/W), and a high-saturation-current (>17 mA). A low level of radio frequency crosstalk between the two photodiodes (less than -15 dB) could also be achieved for a wide frequency range (near DC to 40 GHz). This is low enough for the multichannel receivers in a WDM broadcast system. In addition, by use of our module, we demonstrated digital/analog signals co-transmission and demultiplexing with speeds of 2.5 Gb/s at optical wavelengths of 1530 and 1550 nm.

Au/Ge/Pd ohmic contacts to n-GaAs with the Mo/Ti diffusion barrier

The influences of the As-outdiffusion and Au-indiffusion on the performances of the Au/Ge/Pd/n-GaAs ohmic metallization systems are clarified by investigating three different types of barrier metal structures Au/Ge/Pd/GaAs, Au/Ti/Ge/Pd/ GaAs, and Au/Mo/Ti/Ge/Pd/GaAs. The results indicate that As-outdiffusion leads to higher specific contact resistivity, whereas Au-indiffusion contributes to the turnaround of the contact resistivity at even higher annealing temperature. For Au/Mo/Ti/Ge/Pd/n-GaAs samples, they exhibit the smoothest surface and the lowest specific contact resistivity with the widest available annealing temperature range. Moreover, Auger electron spectroscopy depth profiles show that the existing Ti oxide for the Mo/Ti bilayer can very effectively retard Au-indiffusion, reflecting the onset of the turnaround point at much higher annealing temperature.

Leaky-wave photodiodes with a partially p-doped absorption Layer and a distributed Bragg reflector (DBR) for high-power and high-bandwidth-responsivity product performance

In this letter, we describe a novel edge-coupled photodiode (PD) structure, which can greatly relax the dependence of the responsivity on the cleaved length of an evanescently coupled optical waveguide. The integration of a leaky optical waveguide with a distributed Bragg reflector (DBR) and a partially p-doped photoabsorption layer allows the demonstrated device to exhibit a higher saturation current-bandwidth and responsivity than a control sample without the DBR structure. We achieved excellent speed (40-50 GHz), responsivity (0.8 A/W), and saturation current-bandwidth products (720 mAmiddotGHz at 40 GHz), comparable to the high-performance of an evanescently coupled PD, whose variation of responsivity is more sensitive to the cleaved waveguide length (30% versus 7%) than is our demonstrated device

High-responsivity, high-speed, and high-saturation-power performances of evanescently coupled photodiodes with partially p-doped photo-absorption layer

Electrical bandwidth, output saturation current (power), and responsivity performances are usually three trade-off parameters in the design of high-speed photodetectors. In this paper, we demonstrate a high performance evanescently coupled photodiode (ECPD) with the partially p-doped photo-absorption layer. As compared to the control ECPD with the traditional intrinsic photo-absorption layer, the demonstrated device can exhibit much higher output saturation current (power) and electrical bandwidth without sacrificing the quantum efficiency performance.

High uniformity of Al 0.3 Ga 0.7 As/In 0.15 Ga 0.85 As doped-channel structures grown by molecular beam-epitaxy on 3 GaAs substrates

Al0.3Ga0.7As/ln0.15Ga0.85As doped-channel structures were grown by molecular beam epitaxy on 3″ GaAs substrates. The uniformities of electrical and optical properties across a 3″ wafer were evaluated. A maximum 10% variation of sheet charge density and Hall mobility was achieved for this doped-channel structure. A1 µm long gate field-effect transistor (FET) built on this layer demonstrated a peak transconductance of 350 mS/mm with a current density of 470 mA/mm. Compared to the high electron mobility transistors, this doped-channel FET provides a higher current density and higher breakdown voltage, which is very suitable for high-power microwave device applications.