Search

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.

U-grooved metal-semiconductor-metal photodetectors (UMSM-PD's) 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.

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-PD's). 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.

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.

Aiming at future uses in large silicon tracking devices, 4/spl times/8 cm/sup 2/ silicon microstrip sensors were fabricated, and the processes related to such sensors were studied. The fabrication of 4/spl times/8 cm/sup 2/ silicon microstrip sensors on 100 mm wafers has become a routine procedure with a good yield rate. A 4/spl times/64 cm/sup 2/ long ladder, assembled from eight pieces of 4/spl times/8 cm/sup 2/ sensors, has been tested at the CERN SPS area. Test results show that such a detector is feasible. >

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.

A metal-semiconductor-metal photodetector (MSMPD) with U-shaped interdigitated electrodes and an intrinsic hydrogenated amorphous silicon (i-a-Si:H) heterojunction, fabricated on a p-type [100] Si wafer, was studied. This Si UMSM-PD with a 70 nm i-a-Si:H overlayer, 0.9-/spl mu/m-deep recessed electrodes, and a finger width and spacing of 3 /spl mu/m, had a full-width at half-maximum (FWHM) of 50.8 ps, and a fall-time of 140 ps for its temporal response, a responsivity of 0.18 A/W, as measured with a 830-nm incident laser, a dark current density of 1.5 pA//spl mu/m/sup 2/ and an internal quantum efficiency of 27%. Its performance was much better than that of the conventional Si-based planar MSM-PD. The improved device characteristics were attributed to the U-shaped electrodes which resulted in a stronger lateral, electric field in the light absorption region of the photodetector.

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.

A thin intrinsic hydrogenated amorphous silicon (i-a-Si:H) layer was used to improve the performance of Si metal-semiconductor-metal photodetectors (MSM-PDs). At a bias of 10 V, this a-Si:H MSM-PD had a rise time of 25 ps and an FWHM of 55 ps for temporal response, a dark current density of 690 fA//spl mu/m/sup 2/, a responsivity of 0.7 A/W and a spectral response peaking at 700 nm.

An amorphous metal-semiconductor-metal photodetector with ridged electrodes and an absorption layer of 600 nm of intrinsic hydrogenated amorphous silicon-germanium (i-a-SiGe:H) was fabricated on Corning 7059 glass. The ridged electrodes not only increase the volume of the absorption region but also cause a stronger lateral electric field in the absorption layer and hence effectively increase the responsivity of the device.

To improve the electroluminescence (EL) properties of the a-SiC:H-based pin thin film light-emitting diodes (TFLEDs) with the promotion of hole injection efficiency, a thin Mo metal film was used as a buffer layer to prevent reactions between the ITO (indium-tin-oxide) electrode and the p+-a-Si:H layer. With the formation of semi-transparent Mo silicide after annealing, a lower EL threshold voltage and a significantly higher brightness for a finished TFLED were achieved. The brightness of the obtained device was 1300 cd/m2 at an injection current density of 600 mA/cm2, and its EL threshold voltage was 14 V.

Amorphous silicon (a-Si:H) layers are used to improve the injection current density J and threshold voltage Vth of porous-silicon light-emitting diodes (PS-LEDs). A PS-LED with n-i-n-p-n a-Si:H layers is shown to have a substantially (> 6 orders of magnitude) higher J than that of the PS-LED without any a-Si:H layers. In addition, a lower Vth of 4.2 V and a higher brightness B of 20.5 cd/m2 at J = 600 mA/cm2 are achieved as compared to other PS-LEDs with n-i-p-n a-Si:H layers.

A novel simple bottom-electrode metal-semiconductor-metal photodetector (BMSM-PD) with an i-a-Si:H barrier layer and a phosphorus-doped n-a-Si:H light-absorbing layer was used to improve the responsivity of MSM-PD. At a bias of 10 V and an He-Ne laser incident power of 10 /spl mu/W, the obtained n-a-Si:H BMSM-PD had a high responsivity of 10 A/W, a low dark current density of 2.35 pA//spl mu/m/sup 2/, and a spectral response peaked at 605 nm.