Recently infrared photodetectors have attracted much attention due to their potential use in infrared imaging, optical communications, medical detection and many other fields. In this letter, we report a THz quantum well infrared detector based on AlGaAs/GaAs material system. Structure with 4% Al content in the barrier was grown using molecular beam epitaxy (MBE). The photocurrent spectra were measured at 4.3 K with a Fourier transforming infrared spectrometer using a solid substrate far-IR beam splitter and the peak response wavelength at 46 μm was observed, close to the theoretical calculated results. The dark currents for the THz QWIP detector have been measured at different temperatures. It was found that there is a huge discontinuity in the current. We analyzed this phenomenon and believed the discontinuity in the current was caused by intersubband impact ionization of the first quantum well.
This paper reports the fabrication details of ion-implanted Si:P blocked-impurity band photodetectors with lateral structure. A set of performance data has been measured under the operating temperature of 5.5 K. The device exhibits good blocking characteristics with low dark current density under 10−4 A/cm2. Linear black-body response has been observed at small bias voltage (1 V) and low temperature (5.5 K) with the peak responsivity of 0.8 A/W. The photocurrent (PC) spectra show response peak at 27.3 μm and extend to 40 μm (~7.5 THz), which indirectly proves the feasibility of the preparation of Si:P BIB detectors using ion implantation. In addition, other small features in the PC spectra are designated to associate with the photothermal ionization and the silicon phonon absorption processes. Our work provides an alternative convenient approach to fabricate Si:P BIB detector for far-infrared and terahertz radiation detection.
In this paper, a novel 32×1 ROIC with high dynamic range is presented. The ROIC contains a capacitive transimpedance input amplifier (CTIA integrator), followed by a comparator that set a threshold voltage for comparing the integrating signal. It contains the time-to-threshold information in adding additional dynamic range with a linear voltage ramp input, in addition to the regular integration signal. By the end of integration, if the integration signal is less than the threshold voltage, the integration signal is sampled for readout. When the integrating signal is reached to the threshold voltage before the end of integration, the ramping voltage is stored and later sampled for readout in representing the signal level and a digital flag is set in recording the event of trigger. Thus, a high level signal can be saved before it saturating the integrator. A test chip of 32×1 ROIC is designed and fabricated with 0.35 μm triple metal, double poly CMOS technology. The chip test results prove correct function of the circuit with 3.3 V power supply. The results of tracing one channel show that the dynamic range increases 54 dB with a 10-bit ADC and the readout clock frequency is up to 10 MHz.
Scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) both are capable of
mapping the 2-demensional carrier distribution in semiconductor device structures, which is essential in determining their electrical and optoelectronic performances. In this work, cross-sectional SCM1,2 is used to study the InGaAs/InP P-i-N junctions prepared by area-selective p-type diffusion. The diffusion lengths in the depth as well as the lateral
directions are obtained for junctions under different window sizes in mask, which imply that narrow windows may result in shallow p-n junctions. The analysis is beneficial to design and fabricate focal plane array of near infrared photodetectors with high duty-cycle and quantum efficiency. On the other hand, SSRM provides unparalleled spatial resolution (<10 nm) in electrical characterization3 that is demanded for studying low-dimensional structures. However, to derive the carrier density from the measured local conductance in individual quantum structures, reliable model for SSRM is necessary but still not well established. Based on the carrier concentration related transport mechanisms, i.e.
thermionic emission and thermionic field emission4,5, we developed a numerical model for the tip-sample Schottky
contact4. The calculation is confronted with SSRM study on the dose-calibrated quantum wells (QWs).
Degenerate pump-probe experiments have been performed with HgCdTe and GaInNAs thin films. The differential
transmission versus probe delay time shows a negative value for both films, indicating photoinduced absorption from the
trap states. After the negative minimum the differential transmission resumes to zero with long time constants. A rate
equation formalism has been employed to model the carrier dynamics. The calculations fit the experimental differential
transmission very well. The extracted time constants show that the carriers in the trap states of GaInNAs decay to the
equilibrium state with a single time constant of 1.2 ns, while those in HgCdTe shows two time constants of 0.9 ns and 13
ps, respectively. This implies that there exist two types of deep level traps, fast and slow, in HgCdTe thin films.
For most commonly used GaAs/AlGaAs n-type quantum well infrared photodetectors (QWIPs), the normal incident
absorption is not possible because of the transition rule. The optical grating is required to achieve high absorption
quantum efficiencies. When some gratings are patterned on the metal plate, the polarization direction can be changed
greatly because of the diffraction effect. Finite difference time domain (FDTD) method has been used to investigate the
effect of a reflection metal grating on the couple efficiency previously. However, the authors only take one metal grating
and apply periodic boundary condition along the grating direction due to the computation limit. For a real QWIP system,
such simulation is crude. In this work we consider a real GaAs/AlGaAs QWIP with a wavelength response around 15um
and use FDTD method to investigate the effect of a reflection metal grating on the electric field pattern and the couple
efficiency. The simulating results show that the electric field pattern is not periodic for every metal grating in a real
QWIP system. We have also studied the influence of the substrate thickness and the grating period on the electric field
pattern and the couple efficiency. These results offer a guideline for the design of QWIP.
ZnO nanoparticles had been successfully prepared by annealing the precursors at different temperature, which were produced by the chemical precipitation method. The annealing temperature is a key parameter to prepare ZnO nanoparticles. The microstructure of the resultant nanoparticles was studied by means of XRD, TEM and PL spectra. The ultra-violet emission as observed at room temperature.
Thermal characteristics of heavy-boron-doped Si resistor micro-bridge in infrared (IR) emitters, or so-called IR image
simulators, have been studied with the micro-Raman scattering measurement. By illuminating the Si bridge using microscope-objective-focused intensive laser power and taking the advantage of the suspension nature of the Si bridge, the shone spot has been heated up, resulting in changes in Raman spectrum. By taking into account of Fano interference between the inter-valence-band transitions and the optical phonons, the line-shape of the recorded Si Raman spectrum has been analyzed, yielding the Raman peak position and the intensity ratio of the Stokes to anti-Stokes scatterings. The temperature of the measured point has been calculated using these parameters. Line-scanning Raman measurement along some typical directions and Raman mapping over the complete surface of the Si bridge have been performed and the temperature of each measured point has been determined. Because the boundary conditions are different at different places, the same laser illumination leads to different elevated temperature, revealing the heat conduction capabilities at different parts of the Si bridge. The temperature distribution over the Si bridge has been schematically displayed. A finite element simulation analysis has also been carried out and compared with the experimental data. While the thermal characteristics concluded by the simulation are symmetric and uniform, the experimental results, in addition to the
agreement to the calculated ones in general, give some case-dependent information, which is more important to reflect
the features of actual devices and provides the basis for device design and optimization.