Rong-Heng Yuang

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. >

Overall performance improvement in GaAs MSM photodetectors by using recessed-cathode structure

We report the experimental work on the GaAs metal-semiconductor-metal photodetectors with recessed cathode and/or anode. The recessed-cathode detectors exhibit much superior dc and speed performance to the conventional one because of the enhancement of hole transport in this structure. Full-width at half-maximum and fall time of the temporal response were measured to be 21 and 13 ps at 5 V bias on a 50/spl times/50 /spl mu/m/sup 2/ detector with a finger width and spacing of 3 /spl mu/m.

HIGH-SPEED GAAS METAL-SEMICONDUCTOR-METAL PHOTODETECTORS WITH RECESSED METAL ELECTRODES

The GaAs metal‐semiconductor‐metal photodetector (MSM‐PD) with recessed metal electrodes have been fabricated and characterized. The recessed structure allows very short photocarrier sweep‐out time because of both a strengthened electric field in the active region and a shortened distance for the photocarriers to reach the electrodes. Improved high‐speed performance and enhanced peak amplitude in the temporal response can thus be obtained simultaneously. There is about a 60% and 50% improvement in the fall time and peak amplitude of the temporal response at 5 V bias over the conventional device, respectively. The measured results also show that high‐speed operation can be achieved at a lower bias voltage for the GaAs MSM‐PD with recessed metal electrodes as compared to the conventional one. Two‐dimensional simulation was carried out to give an insight into the operation principle of this device.

High-speed InGaAs metal-semiconductor-metal photodetectors with improved responsivity and process yield

High-performance In0.9Ga0.1P-InP-InGaAs metal-semiconductor-metal photodectors with semi-transparent Au Schottky contacts are fabricated and studied. The devices, with an active area of 50×50 μm2 and different finger spacings of 2, 3 and 4 μm, all exhibit high responsivities over 0.7 AW-1 and low dark currents below 10 nA. Extremely linear photoresponse without low frequency internal gain is also observed in these devices. The novel fabrication process used in this work is simple and has nearly 100% high yield. A device with a small finger spacing has also been demonstrated to have improved speed performance without sacrificing its responsivity.

Reduction of hole transit time in GaAs MSM photodetectors by p-type /spl delta/-doping

The temporal responses of the undoped, n-type, and p-type /spl delta/-doped GaAs metal-semiconductor-metal photodetectors were systematically studied. The full-width at half-maximum of the temporal response is significantly improved at low bias for the /spl delta/-doped detectors compared to the conventional undoped one. The p-type /spl delta/-doped detector exhibits the smallest fall-time, and hence the highest bandwidth, because the induced electric field in the absorption region facilitates the transport of the photo-generated holes. In addition, the p-type /spl delta/-doped detector also gives the highest peak amplitude of the temporal response. Two dimensional simulation on the internal electrical field distribution in the detectors is consistent with the experimental results.

GaAs MSM photodetectors with recessed anode and/or cathode

The GaAs metal-semiconductor-metal photodetectors (MSM-PDs) with recessed electrodes have been systematically characterized. The recessed cathode results in effective collection of the speed-limiting holes due to both a strengthened electric field and a shortened transit path around the absorption region while the recessed anode gives no significant change on the electric field distribution, as evidenced by the two dimensional simulation. The experimental results show that the MSM-PDs having the recessed-cathode structure, compared with the conventional one, exhibit a substantial improvement on the speed, peak amplitude, and capacitance, especially at low-bias operation. The fall time of the temporal response approaches its saturation value of about 10 ps at a bias voltage as low as 3 V on the 50 /spl mu/m/spl times/50 /spl mu/m detector with a finger width and spacing of 2 /spl mu/m.

GaAs metal‐semiconductor‐metal photodetectors (MSM‐PD'S) with AlGaAs cap and buffer layers

Abstract GaAs metal‐semiconductor‐metal photodetectors with AlGaAs cap and buffer layers have been fabricated and studied. It is shown that the trap‐induced effects which result from the GaAs surface trap states can be avoided by adding an AlGaAs cap layer. In addition, we used an AlGaAs buffer layer to reduce the interfacial charge effects between the GaAs substrate and the GaAs absorption layer. The dark currents were less than 1 nA and the low frequency internal gain was dramatically improved. The results also show that a complete depletion can occur even at biases below 0.5 V.

The effects of AlGaAs cap layers on the dc and speed performance of GaAs metal-semiconductor-metal photodetectors

The effects of AlGaAs cap layers for GaAs metal-semiconductor-metal photodetectors (MSM-PDs) have been investigated. By changing the thickness of the AIGaAs cap layer (i.e. 30 nm, 60 nm and 90 nm), both DC and speed performance are analyzed and discussed. Meanwhile, two cap structures with abrupt and graded hetero-junction, respectively, were also grown for comparison. The results of this work show that adding a 30 nm-thick AIGaAs cap layer can greatly suppress the low frequency internal gain and lead to improved linearity. At 5 V bias, the rise time and the full-width at half maximum (FWHM) of such 100 /spl mu/m x 100 /spl mu/m devices are measured to be 28 ps and 39 ps, respectively, corresponding to a bandwidth exceeding 10 GHz. The devices with a thicker cap layer, however, have significant internal gain and lower speed response due to the formation of a thicker barrier blocking the photocarriers to reach the electrodes.