Wen-Chin Tsay

Characteristics of MSM photodetectors with trench electrodes on p-type Si wafer

U-grooved metal-semiconductor-metal photodetectors (UMSM-PDs) having various trench depths of interdigitated electrodes and an intrinsic hydrogenated amorphous silicon (i-a-Si:H) to c-Si heterojunction have been fabricated successfully on a p-type [100] Si wafer. The U-grooved structures on c-Si were achieved with a simple orientation-dependent etching (ODE) process. Some important characteristics of the obtained UMSM-PDs are presented and discussed. An UMSM-PD with a 70 nm i-a-Si:H overlayer, 1.45 /spl mu/m-deep recessed electrodes, and 3 /spl mu/m finger width and spacing, had a full width at half maximum (FWHM) of 50.6 ps and a full-time of 132 ps for its temporal response under a bias of 15 V. The significant improvements of transient response for UMSM-PD, as compared to the conventional one, were attributed to the trench electrodes resulted in a stronger lateral electric field in the light absorption region of photodetector. At a bias of 20 V, this UMSM-PD had a responsivity of 0.25 A/W as measured with an 0.83-/spl mu/m incident semiconductor laser, a high photo/dark current ratio about 2000, and an internal quantum efficiency of 36%. This high photo/dark current ratio would be due to the additional i-a-Si:H overlayer on Si wafer. These mentioned performances were much better than those of the conventional Si-based planar MSM-PD.

Optoelectronic characteristics of a-SiC:H-based P-I-N thin-film light-emitting diodes with low-resistance and high-reflectance N/sup +/-a-SiCGe:H layer

The graded-gap a-SiC:H-based p-i-n thin-film light-emitting diodes (TFLEDs) with an additional low-resistance and high-reflectance n/sup +/-a-SiCGe:H layer were proposed and fabricated on indium-tin-oxide (ITO)-coated glass substrate in this paper. For a finished TFLED, a brightness of 720 cd/m/sup 2/ could be obtained at an injection current density of 600 mA/cm/sup 2/, and its EL (electroluminescence) threshold voltage was lowered to 8.6 V. In addition, the effects of reflectance and resistance of a-SiCGe:H film on the performance of TFLED were discussed. The optimum rapid thermal annealing (RTA) conditions for fabrication of TFLED after metallization were also studied and employed to improve the optoelectronic characteristics of TFLED.

Improved process of fabricating AC-coupled silicon micro-strip sensors

Abstract A single-sided silicon sensor with capacitors coupling and polysilicon bias resistors has been designed and fabricated. A proposed process with ONO (Oxide-Nitride-Oxide) replacing the usual SiO 2 layer as the dielectric of coupling capacitor, in conjunction with a reordering of sequence for layer formations, is to produce sensors with self-moisture-protection and free from the effect of pin holes. A comparison of presented data of IV, CV and RV measurements for the sensors with ONO and with SiO 2 dielectrics revealed that the ONO processes could lead to an excellent voltage-handling capability of the coupling capacitor. One sensor has been successfully tested twice in the beam at CERN in the past two years, yielding an S/N ratio of 20 and an efficiency above 95%, also demonstrating its excellent stability with respect to lengthy exposure to atmosphere.

HYDROGENATED AMORPHOUS-SILICON CARBIDE P-I-N THIN-FILM LIGHT-EMITTING-DIODES WITH BARRIER LAYERS INSERTED AT P-I INTERFACE

To improve the electroluminescence (EL) intensity of the hydrogenated amorphous silicon carbide (a-SiC:H) pi-n thin-film light-emitting diode (TFLED), a barrier-layer (BL) structure had been inserted at its p-i interface and used to enhance the hole injection efficiency of TFLED under forward-bias operation. Two TFLEDs with different BL structures were studied. The device 1 had a 25 A i-type single-barrier structure and the device II had an i-type double-barrier structure of barrier(10 A)/well(10 A)/barrier(10 A). The obtainable brightness of device I was 342 cd/m 2 at an injection current density of 600 mA/cm 2 . On the other hand, the device II had a brightness of 256 cd/m 2 at 800 mA/cm 2 . These brightnesses were about 3 orders of magnitude higher than that of a basic a-SiC:H p-i-n TFLED

Characteristics of Si-based MSM photodetectors with an amorphous-crystalline heterojunction

Abstract Various amorphous silicon alloy films (i.e. i-a-Si:H, i-a-Si 0.65 Ge 0.35 :H, and i-a-Si 0.56 C 0.44 :H) were deposited on crystalline silicon (c-Si) wafers to form amorphous-crystalline heterojunctions which could be used to enhance the performance of planar Si-based metal-semiconductor-metal photodetectors (MSM-PDs). The photocurrents (dark currents) of the fabricated devices were slightly (significantly) lower than that of the MSM-PD without amorphous layer, and the FWHM (full-width at half-maximum) of the temporal response for MSM-PD could be reduced by employing an amorphous film. Experimentally, at a bias voltage of 20 V and for a 830 nm incident semiconductor laser power of 10 μW, the Si-based MSM-PD with a 50 × 50 μ m 2 active area and an i-a-Si 0.65 Ge 0.35 :H overlayer had a responsivity of 0.35 A W −1 , a low dark current density of 0.4 pA μm −2 , a narrower FWHM of 53 ps, and a shorter transient tail of 399 ps for its temporal response. The spectral response of a Si-based MSM-PD with an additional amorphous overlayer had a peak around 700 nm, and covered the range 500–900 nm including 830 nm.

POROUS SILICON LIGHT-EMITTING DIODE WITH TUNABLE COLOR

Abstract We successfully combined porous silicon and amorphous silicon together to fabricate a light-emitting diode, whose emitting color was tunable with different applied voltage. When the applied voltage increased from 30 to 90 V, the emitting color of the device could change from red to blue.

ELECTROLUMINESCENCE OF A-SIC-H P-I-N THIN-FILM LIGHT-EMITTING-DIODES WITH QUANTUM-WELL-INJECTION STRUCTURES

Abstract In order to improve the electroluminescence (EL) characteristics of hydrogenated amorphous silicon carbide (a-SiC:H) p-i-n thin-film light-emitting diodes (TFLEDs), the quantum-well-injection (QWI) structures have been incorporated into their intrinsic (i-) layer. Two types of TFLED were fabricated to study the effect of the incorporated QWI structures on their EL characteristics: the device I contains a step-gap QWI structure of barrier (15 A)/well (45 A)/barrier (15 A) inserted at both the p-i and i-n interfaces, and the device II has only one graded-gap QWI structure of barrier (10 A)/well (10 A)/barrier (10 A) inserted at the p-i interface. The obtained brightness of device I was about 10 cd/m2 at an injection current density of 1 A/cm2. The emission light of device I was yellow-like as detected by human eyes. Whereas, for device II, the brightness was about 256 cd/m2 at 800 mA/cm2 and an orange light emission was observed.

Studies on reducing leakage current of large-area silicon microstrip sensors

8/spl times/4 cm/sup 2/ single-sided p/sup +/-i (or v)-n/sup +/ silicon microstrip sensors with coupling capacitors and polysilicon bias resistors were fabricated with the planar technology, and various techniques used to reduce the leakage currents of sensors and their results are presented. Different gettering processes have been employed to remove the impurities and defects from the sensor active regions, and the Electronic Research and Service Organization (ERSOs) Charge-Coupled Device (CCD) gettering technique, combined with backside polysilicon and oxide-nitride-oxide (ONO) deposition process, was found to be the most effective and suitable one. From the measurement results of the special p/sup +/-i (or v)-n/sup +/ junction test structures, it was found that the sensor leakage current mainly came from the side-wall leakage of its p/sup +/-strip. A modified LOCal Oxidation of Silicon (LOGOS) isolation process has been used to reduce this side-wall leakage. Also, the Sirtl-etch analysis of the sensor revealed that the side-wall leakage current has been caused by residual boron-implantation defects after annealing. These defects would concentrate along the edge of p/sup +/-strip and be enhanced to cause dislocations by the film-edge-induced stress effect. Several annealing techniques have also been studied to remove the boron-implantation damages. The fabricated prototype sensors have been tested in a beam at the CERN Super Proton Synchrotron area. The test results showed that the sensor concept under study is feasible.

Fabrication of double-metal AC-coupled silicon microstrip detectors

Abstract The 8 × 4 cm 2 single-sided double-metal p + -i-n + silicon microstrip detectors (SMDs) with coupling capacitors and polysilicon bias resistors were fabricated with the newly developed double-metal processing techniques with different inter-metal dielectrics. The results of using these processing techniques and some features of double-metal process are reported. The characteristics of polysilicon bias resistors obtained with BF 2 ion-implantations having various doses and their effects on the leakage currents of SMDs have also been studied.

Studies on reducing leakage current of large-area silicon PIN microstrip sensors-methods to prevent implantation damage

Several 8/spl times/4 cm/sup 2/ single-sided silicon microstrip sensors with capacitor coupling and polysilicon bias resistors have been fabricated by using planar technology. Sirtl etch analysis revealed that the leakage current was caused by implantation damage. A boron solid source predeposition process has been developed to replace the p/sup +/ strip implantation. Several anneal technologies have been studied to remove the implantation damge. The prototype sensors have been tested at the CERN SPS area. Test results showed that such a sensor is feasible.