B.-C. Hsu

A novel photodetector using MOS tunneling structures

A metal/oxide/p-Si structure with ultrathin oxide is utilized as a photodetector. At positive gate bias, the dark current of the photodetector is limited by the thermal generation of minority carriers in the inversion layer. The high growth temperature (1000/spl deg/C) of the gate oxide can reduce the dark current to a level as low as 3 nA/cm/sup 2/. As biased in the inversion layer, the tunneling diode works in the deep depletion region with soft pinning of oxide voltage, instead of the pinning of surface potential, very different from the conventional MOS diode with thick oxide.

A high efficient 820 nm MOS Ge quantum dot photodetector

A Ge quantum dot photodetector has been demonstrated using a metal-oxide-semiconductor (MOS) tunneling structure. The oxide film was grown by liquid phase deposition (LPD) at 50/spl deg/C. The photodetector with five-period Ge quantum dot has responsivity of 130, 0.16, and 0.08 mA/W at wavelengths of 820 nm, 1300 nm, and 1550 nm, respectively. The device with 20-period Ge quantum dot shows responsivity of 600 mA/W at the wavelength of 850 nm. The room temperature dark current density is as low as 0.06 mA/cm/sup 2/. The high performance of the photodetectors at 820 nm makes it feasible to integrate electrooptical devices into Si chips for short-range optical communication.

A comprehensive study of inversion current in MOS tunneling diodes

The gate current of MOS tunneling diodes biased at inversion region with different substrate doping is investigated. For p-type substrate (1-5 /spl Omega/-cm) devices, the tunneling diode works in the deep depletion region and the inversion current is dominated by the thermal generation rate of minority electrons via traps at Si/SiO/sub 2/ interface and in the deep depletion region. The activation energy is approximately equal to half of the silicon bandgap independent of gate voltage. For devices on p/sup +/ substrate (0.01-0.05 /spl Omega/-cm), the band-to-traps tunneling and band-to-band tunneling are the dominating current components at inversion bias, and reveal a strong field dependence and a weak temperature dependence. The band-to-traps and band-to-band current components are even more significant in the devices on the p/sup ++/ substrate (0.001-0.0025 /spl Omega/-cm). Finally, the effects of temperature and light illumination on inversion current of MOS tunneling diodes will be also discussed.

A PMOS tunneling photodetector

A metal/oxide/n-Si structure with ultrathin gate oxide is utilized as a photodetector. At inversion gate bias, the dark current and photocurrent are determined by both the minority carrier (hole) generation rate in the deep depletion region and the electrons tunneling from the gate electrode to n-type Si, while only the former component is significant in the NMOS photodetector. The electron tunneling current dominates the photocurrent at sufficiently large negative gate voltage, and the sensitivity of PMOS detectors is, therefore, enhanced by approximately one order of magnitude, as compared to NMOS detectors.

Novel MIS Ge-Si quantum-dot infrared photodetectors

The metal-insulator-semiconductor (MIS) Ge-Si quantum-dot infrared photodetectors (QDIPs) are successfully demonstrated. Using oxynitride as gate dielectric instead of oxide, the operating temperature reaches 140 and 200 K for 3-10 and 2-3 /spl mu/m detection, respectively. From the photoluminescence spectrum, the quantum-dot structures are responsible for the 2-3 /spl mu/m response with high operation temperature, and the wetting layer structures may be responsible for the 3-10 /spl mu/m response. This novel MIS Ge-Si QDIP can increase the functionality of Si chip such as noncontact temperature sensing and is compatible with ultra-large scale integration technology.

Recessed Oxynitride Dots on Self-Assembled Ge Quantum Dots Grown by LPD

Recessed oxynitride dots deposited on self-assembled Ge dots are demonstrated using liquid-phase deposition (LPD). By adding ammonia into the solution, the nitrogen atoms can be incorporated into the deposited film. The tensile strain of the Si cap layer directly deposited on Ge dots can enhance the oxynitride nucleation and deposition on Si surface. The tensile strain may also increase the etching rate of the Si cap layer and the recessed dots are formed directly above the Ge dots. The LPD-SiON dots have a higher dot step height as compared to LPD-SiO 2 dots.

Growth and Electrical Characteristics of Liquid-Phase Deposited SiO2 on Ge

The liquid-phase deposition (LPD) of SiO 2 at 50°C on Ge substrates is investigated. Silicic acid (SiO 2 .xH 2 O) is used to saturate hydrofluorosilicic acid at 30°C and this shortens the time required for solution preparation to 3 h. The growth rate of LPD oxide on Ge is much slower than that of LPD oxide on Si at the beginning of the deposition process, while surface roughness of LPD oxide on Ge is larger than that of LPD oxide on Si. A metal-oxide-semiconductor tunneling diode on Ge is fabricated using the LPD oxide. The tunneling current of the Ge diodes at inversion bias increases as LPD oxide thickness increases, indicating that the trap density in the LPD oxide increases with increasing oxide thickness, and the current transport is dominated by the trap assistant tunneling.

Oxide roughness effect on tunneling current of MOS diodes

Two-dimensional (2-D) device simulation is used to investigate the tunneling current of metal ultra-thin-oxide silicon tunneling diodes with different oxide roughness. With the conformal nature of ultrathin oxide, the tunneling current density is simulated in both direct tunneling and Fowler-Nordheim (FN) tunneling regimes with different oxide roughness. The results show that oxide roughness dramatically enhances the tunneling current density and the 2-D electrical effect is responsible for this increment of tunneling current density. Furthermore, a set of devices with controlled oxide roughness is fabricated to verify the simulation results and our model qualitatively agrees with the experiment results.

High efficient 820 nm MOS Ge quantum dot photodetectors for short-reach integrated optical receivers with 1300 and 1550 nm sensitivity

A metal-oxide-semiconductor (MOS) Ge quantum dot photodetector is demonstrated. The oxide is grown directly on Ge substrate by liquid phase deposition (LPD). The photodetector has the responsivity of 130, 0.16, and 0.08 mA/W under the wavelength of 820 nm, 1300 nm, and 1550 nm, respectively. The dark current is extremely low (0.06 mA/cm/sup 2/). The high performance of Ge quantum dot MOS photodetectors at 820 nm makes it feasible to integrate optoelectronic devices into the Si chip for short-reach optical communication.

Roughness-enhanced reliability of MOS tunneling diodes

Both electrical and optical reliabilities of PMOS and NMOS tunneling diodes are enhanced by oxide roughness, prepared by very high vacuum prebake technology. For rough PMOS devices, as compared to flat PMOS devices, the Weibull plot of T/sub BD/ shows a 2.5-fold enhancement at 63% failure rate, while both the D/sub 2/ and H/sub 2/-treated flat PMOS devices show similar inferior reliability. For rough NMOS devices, as compared to flat NMOS devices, the Weibull plot of T/sub BD/ shows a 4.9-fold enhancement at 63% failure rate. The time evolutions of the light emission from rough PMOS and NMOS diodes degrade much less than those of flat PMOS and NMOS diodes. The momentum reduction perpendicular to the Si/SiO/sub 2/ interface by roughness scattering could possibly make it difficult to form defects in the bulk oxide and at the Si/SiO/sub 2/ interface by the impact of the energetic electrons and holes.