Tomohiro Morishita

High-Sensitivity Temperature Measurement With Miniaturized InSb Mid-IR Sensor

This paper reports the development and evaluation of an InSb photovoltaic infrared sensor (InSb PVS) operating at room temperature. The InSb PVS consists of 700 InSb p⁺ - p^- - n⁺ photodiodes connected in series, on a semi-insulating GaAs (100) substrate. An Al_0.17rIn_0.83Sb barrier layer between p⁺ and p^- layers was used to reduce diffusion of photo-excited electrons. Cutoff wavelength was 6.8 mum and output signal was almost linear with irradiance up to 0.6 mW/cm². Sensitivity of 67 muV/K and noise equivalent temperature difference of 2.2 mK/Hz^1/2 was obtained at room temperature, which shows the sensor to be a suitable for noncontact thermometry.

Direct Measurements of Femtosecond Energy Dissipation Processes of Hot Electrons in a Gold Film

Energy dissipation processes of hot electrons in a gold thin film were measured by a femtosecond time-resolved transient reflecting grating method. The processes were analyzed using the two-temperature model and the theory of the transient grating method. It was found that the electron-phonon coupling and thermal diffusion processes could be investigated independently. Temperature dependence of the electron-phonon coupling factor and the thermal conductivity was investigated quantitatively. The results suggested that the nonthermal states of hot electrons still contribute to the dissipation processes on time scales of several picoseconds.

Performance Improvement of Molecular Beam Epitaxy Grown InSb Photodiodes for Room Temperature Operation

In this paper, we report the optimization of the light absorber layer thickness of InSb p+–p-–n+ photodiodes grown by molecular beam epitaxy (MBE) on GaAs(001) substrates. An Al0.17In0.83Sb barrier layer between p+ and p- layers was used to reduce the diffusion of photoexcited electrons, allowing rectifying characteristics and high photovoltage response at room temperature. Photodiodes with a junction area of 90×90 µm2 and p--layer thicknesses varying from 0.5 to 3 µm were fabricated, demonstrating that photocurrent increased with p--layer thickness, which is in good agreement with theoretical calculations. However, the non biased differential resistance did not increase as expected, possibly owing to an increase in film defect density with increasing film thickness, which is considered to produce leakage paths through the light absorber layer. Despite the presence of defects on the grown films, photodiodes with a p--layer thickness of 3 µm showed a sixfold improvement in the signal-to-noise ratio when compared with that of 0.5 µm.

Ultrafast electron transport phenomena in highly excited gold films

Abstract Non-equilibrium dynamics of hot electrons in highly excited gold films has been investigated by using the femtosecond transient reflecting grating method. Transport processes which compete with electron–phonon coupling processes were investigated by observing thermal surface displacements. The results were compared with calculations by a simple thermoelastic equation and the two-temperature model with two different conditions for the thermal conductivity. The results suggested that non-thermal states of the hot electrons still contribute transport processes on time scales of several picoseconds.

Miniaturized InSb Mid-JR Sensor for Room Temperature Operation

This paper reports the development and evaluation of an InSb photovoltaic infrared sensor (InSb PVS) operating at room temperature. The InSb PVS consists of 700 InSb p⁺-p^--n⁺ photodiodes connected in series, on a semi-insulating GaAs (100) substrate. An Al_0.17In_0.83Sb barrier layer between p⁺ and p^- layers was used to reduce diffusion of photo-excited electrons. Cutoff wavelength was 6.8 mum and output signal was linear with incident irradiance. Noise equivalent temperature difference (NETD) of 2.2times10^-3 degC/Hz^1/2 was obtained at room temperature, which shows the sensor to be a promising device for human body detection or non-contact thermometry.