M Yoneoka

Impact of neutron irradiation on optical performance of InGaAsP laser diodes

Abstract Results are presented of an extended study on the degradation and recovery behavior of optical and electrical performance and on induced lattice defects of 1.3 μm InGaAsP double channel planar buried heterostructure laser diodes with an In 0.76 Ga 0.24 As 0.55 P 0.45 multi-quantum well active region, subjected to a 1 MeV fast neutron and 1 MeV electron irradiation. The degradation of the device performance increases with increasing fluence. Two hole capture traps with near midgap energy level in the In 0.76 Ga 0.24 As 0.55 P 0.45 multi-quantum well active region are observed after a 1×10 16 n/cm 2 irradiation. These deep levels are thought to be associated with a Ga vacancy. The decrease of optical power is related to the induced lattice defects, leading to a reduction of the non-radiative recombination lifetime and of the carrier mobility due to scattering. The difference in radiation damage between 1 MeV fast neutrons and 1 MeV electrons is discussed taking into account the non-ionizing energy loss (NIEL). The radiation source dependence of performance degradation is attributed to the difference of mass and the probability of nuclear collision for the formation of lattice defects. The decreased optical power recovers by thermal annealing, and the recovery increases with increasing annealing temperature. The optical power recovers by 45% for 1 MeV neutron irradiation with a fluence of 1×10 15 n/cm 2 after a 300°C annealing.

Effects of mechanical stress on polycrystalline-silicon resistors

Abstract Results are presented of a study on the mechanical stress dependence of the resistance of polycrystalline silicon (Poly-Si) films doped with different atomic species, namely, with boron and phosphorus ions. B-doped films of 400 nm and P-doped films of 250 nm thickness were deposited by low-pressure chemical vapor deposition at 620 °C on thermally oxidized silicon wafers. A controlled amount of external stress was applied to the silicon wafers in order to investigate the impact on the electrical performance of the implanted Poly-Si resistors. The resistance of the B-doped Poly-Si films is shown to increase by the mechanical stress, while the resistance of the P-implanted Poly-Si films remained unchanged. It is concluded that this difference is related to the structural differences between Poly-Si films implanted with boron and phosphorus, respectively.

Radiation damage of N-MOSFETS fabricated in a BiCMOS process

Results are presented of a study on the radiation damage and its recovery behavior resulting from thermal annealing of n-MOSFETs fabricated in a 0.8-μm single-well BiCMOS process, subjected to γ-rays, 1-MeV electrons and 1-MeV neutrons. After irradiation, the base (substrate) current and interface trap density normally increase with increasing fluence. This result points out that both ionization damage in the gate oxide and lattice defects in the p-well are induced by the irradiation. The interface trap density recovers by 85% for γ-ray irradiation with a fluence of 1×108 rad, after a 300 °C annealing.

Hole trap distribution on 2 MeV electron irradiated high-k dielectrics

The effects of 2 MeV electron irradiation on the electrical properties of high-k dielectric based metal–insulator–semiconductor capacitors have been studied. Samples consist of 5.9 nm-thick films of aluminum oxide and hafnium oxide deposited by atomic layer deposition on silicon substrates. Deep-level transient spectroscopy (DLTS) and admittance measurements reveal that electron irradiation modifies the defect density of both surface states at the dielectric–semiconductor interface and border traps existing inside the dielectric. The experimental results indicate that irradiation has a double effect. The incident electrons transfer their energy and generate additional surface states, leading to a degradation of the interface. On the other hand, irradiation generates electron–hole pairs inside the dielectric. Some of the holes are trapped by border traps located inside the dielectric at locations close to the interface. As a result, border traps capturing holes are neutralized and become inactive after irr...

Evaluation of Degradation due to Electron Irradiation of Si1-xCx S/D n-type MOSFETs

To solve the problem of the limitation to improve device performance in standard Si integration technologies and to develop radiation-harsh devices, the irradiation effects of Si1-xCx source/drain (S/D) n-type metal oxide semiconductor field effect transistors (n-MOSFETs) have been investigated. It is shown that the drain current and the maximum electron mobility of Si1-xCx n-MOSFETs decrease by electron irradiation. The reduction of the device performance can be explained by the radiation-induced lattice defects in the devices. However, the electron mobility enhancement effect by adding C remained after an electron irradiation up to 5×1017 e/cm2.

Increased Radiation Hardness of Short-Channel Electron-Irradiated Si1-xGex Source/Drain p-Type Metal Oxide Semiconductor Field-Effect Transistors at Higher Ge Content

In this work, it is shown that the maximum hole mobility of compressively strained Si1-xGex source–drain (S/D) p-MOSFETs is degraded after high-fluence 2 MeV electron irradiation, suggesting the loss of strain in the Si channel caused by the radiation-induced displacement damage. This is supported by the fact that the mobility reduction after irradiation is larger for SiGe S/D devices than for Si references at the same fluence (5×1017 cm-2) and becomes more pronounced for shorter gate lengths. At the same time, however, it is found that the extent of mobility reduction becomes smaller for p-MOSFETs with a higher Ge content (35%, compared with 20 or 30%). Finally, it is concluded that, for shorter devices, the displacement-damage-related degradation mechanism becomes less pronounced with increasing Ge content in Si1-xGex S/D regions.

Gate-Length Dependent Radiation Damage in 2-MeV Electron-Irradiated Si1-xGex S/D p-MOSFETs

The effect of 2-MeV electron irradiation of Si1-xGex S/D p-MOSFETs with different gate length and Ge concentration is studied. After electron irradiation, the maximum hole mobility decreases with increasing electron fluence for all gate lengths. In particular, after 5 x 1017e/cm2 irradiation, the maximum hole mobility drastically decreases at short channel region for x = 0.3. Furthermore, a negative shift of the threshold voltage is clearly observed. These degradations can be explained both by the lattice defects and the stress relaxation in the Si channel created by atomic displacements.