Homojunction Far-infrared Detectors Research Articles

Performance optimization of resonant cavity enhanced n-GaAs homojunction far-infrared detectors: A theoretical study

The n-GaAs homojunction interfacial workfunction internal photoemission (HIWIP) far-infrared (FIR) detector is investigated to improve the quantum efficiency by simulation. The main structure, the bottom mirror, and the top mirror for the resonant cavity enhanced detector are optimized step by step. Two designs of the bottom mirror are suggested and compared. One consists of a bottom contact layer and one period of undoped/doped GaAs layers; the other is composed of a bottom contact layer, an undoped GaAs layer, and a gold layer. The results show that both mirrors enhance the quantum efficiency significantly and the gold mirror seems to be a better choice if not considering the technical difficulty. Preliminary study of the top mirror is also conducted. The top mirror shows a satisfactory effect under the condition that the reflectivity of the bottom mirror is high enough. The resulting quantum efficiency can be as high as 29.0% theoretically, which is much higher than p-GaAs and Si HIWIP FIR that was ever reported.

Design of bottom mirrors for resonant cavity enhanced GaAs homojunction far-infrared detectors

The design of bottom mirrors for resonant cavity enhanced (RCE) GaAs homojunction far-infrared (FIR) detectors has been investigated in the framework of three possible projects. The results show that neither the bottom contact layer of the detector itself nor the distributed Bragg reflector, which has been widely employed in near- and mid-infrared detectors, can perform well as bottom mirrors for FIR detectors. A new kind of bottom mirrors based on undoped/doped GaAs layers is proposed and optimized. Though the absorption cannot be neglected, the bottom mirror shows a satisfactory effect. The resulting absorption probability (as well as the quantum efficiency) in the detector cavity for this kind of RCE p -GaAs FIR detector is three times of the normal p -GaAs homojunction FIR detector demonstrated experimentally. This kind of bottom mirror design opens a new way to increase the quantum efficiency in homojunction FIR detectors.

Demonstration of bottom mirrors for resonant-cavity-enhanced GaAs homojunction far-infrared detectors

A proposal for the bottom mirrors of resonant-cavity-enhanced GaAs homojunction far-infrared (FIR) detectors has been suggested and optimized based on undoped/doped GaAs layers with the Fresnel matrix method. With this kind of bottom mirror, the calculated absorption probability in the detector cavity increases two times over that in the normal detector structure. Comparing optical measurements have been carried out on n-GaAs homojunction FIR detector structures with and without the bottom mirrors, as well as a single optimized bottom mirror structure (without the detector cavity structure). The experimental FIR reflection and transmission results demonstrate well the theoretical design.

Study of band gap narrowing effect in n-GaAs for the application of far-infrared detection

The band gap shrinkage Δ E g of n-GaAs in relation with the doping concentration ( N) is still controversial in various theories and experiments. Most of the experimental results of Δ E g from photoluminescence have already been questioned to have an overestimation by a few tens of meV. We have carried out detailed temperature-dependent transmission experiments on an n-GaAs homojunction far-infrared (FIR) detector structure. By calculating the transmission spectra taking into account the band tail effect, we obtained a 1/3 power rule of Δ E g in n-GaAs by Δ E g=−3.60×10 −8 (eV cm) N 1/3. Our results support Harmon et al.'s experimental Δ E g results from the electrical measurements of np product in n-GaAs (Appl. Phys. Lett. 64 (1994) 502). The yielded Δ E g is employed to calculate the cut-off wavelength λ c and dark current of n-GaAs homojunction FIR detectors to investigate the potential application. We find that n-GaAs is more suitable for a long λ c detector design, and has a similar dark current behavior with that of Si and p-GaAs homojunction FIR detectors.

Study on the quantum efficiency of resonant cavity enhanced GaAs far-infrared detectors

We present a detailed theoretical analysis on the quantum efficiency of a resonant cavity enhanced (RCE) GaAs homojunction work function internal photoemission far-infrared (FIR) detector. The quantum efficiency under both resonant and nonresonant conditions has been calculated. All the detector parameters are optimized under the realistically nonresonant condition. The further investigation of the standing wave effect (SWE) shows that the SWE is important and cannot be neglected for the FIR detector. The resulting quantum efficiency is about two times higher than that in the normal GaAs homojunction FIR detector measured by experiment, showing a promising effect. In contrast to the case in the near-infrared region, the wavelength selectivity is not obvious in the FIR region. The theoretical analysis can be applied to other RCE homojunction FIR detectors.

Radiative recombination characteristics in GaAs multilayer n+−i interfaces

In this communication, we have carried out a detailed investigation of radiative recombination in n-GaAs homojunction far-infrared detector structures with multilayer emitter (n+)-intrinsic (i) interfaces by temperature-dependent steady-state photoluminescence measurements. The observation of the emitter-layer luminescence structures has been identified from their luminescence characteristics, in combination with high density theoretical calculation. A photogenerated carrier transferring model has been proposed, which can well explain the dependencies of the luminescence intensities on the laser excitation intensity and temperature. Furthermore, the obtained radiative recombination behavior helps us to offer a proposal to improve the operating temperature of the detector.

Effect of interface states on negative capacitance characteristics in GaAs homojunction far-infrared detectors

Bias-, frequency- and temperature-dependent capacitance characteristics of p-GaAs homojunction interfacial work-function internal photoemission (HIWIP) far-infrared detectors are reported. A strong negative capacitance phenomenon has been observed. The origin of this effect is believed to be due to the carrier capture and emission at interface states, and has been confirmed by a comparison study of capacitance characteristics on p-GaAs HIWIP detectors with different interface state densities. A fitting data based on charging–discharging current and the inertial conducting current model show good agreement with the experimental observations.

Negative capacitance of GaAs homojunction far-infrared detectors

Bias, frequency and temperature-dependent capacitance characteristics of p-GaAs homojunction interfacial work-function internal photoemission (HIWIP) far-infrared detectors are reported. A strong negative capacitance phenomenon has been observed. Unlike in other devices, even up to 1 MHz in HIWIP, the negative capacitance value keeps increasing with frequency, giving a stronger effect. The origin of this effect is believed to be due to the carrier capture and emission at interface states. Fitting data based on charging-discharging current and the inertial conducting current model show good agreement with the experimental observations.

Low-frequency noise and interface states in GaAs homojunction far-infrared detectors

Low-frequency noise characteristics of p-GaAs homojunction interfacial work-function internal photoemission (HIWIP) far-infrared (FIR) detectors are reported. The noise was found to exhibit 1/f behavior related to interface states at frequencies below 1 kHz and frequency independent shot noise at higher frequencies. The noise expressions correctly predict the dark current noise behavior, and provide a means of estimating both the gain and energy distribution of the interface states. The interface state density is estimated to be in the order of 10/sup 11/ cm/sup -2/. It has been shown that the estimated gain and noise equivalent power are in good agreement with the previous results obtained via optical measurements.

Demonstration of Si homojunction far-infrared detectors

A 48 μm cutoff wavelength (λc) Si far-infrared (FIR) detector is demonstrated. Internal photoemission over a Si interfacial work-function of a homojunction consisting of molecular beam epitaxy grown multilayers (p+ emitter layers and intrinsic layers) is employed. The detector shows high responsivity over a wide wavelength range with a peak responsivity of 12.3±0.1 A/W at 27.5 μm and detectivity D* of 6.6×1010 cmHz/W. The λc and bias dependent quantum efficiency agree well with theory. Based on the experimental results and the model, Si FIR detectors (40–200 μm) with high performance and tailorable λcs can be realized using higher emitter layer doping concentrations.

Effect of emitter layer concentration on the performance of GaAs p/sup +/-i homojunction far-infrared detectors: a comparison of theory and experiment

The performance of GaAs multilayer (p/sup +/-i-p/sup +/-i-...) homojunction interfacial workfunction internal photoemission (HIWIP) far-infrared (FIR) detectors as a function of emitter layer (p/sup +/) concentration is reported. The dark current characteristics have been investigated and compared with a model which includes the space charge, tunneling, and multiple-image-force effects. The experimentally determined detector cutoff wavelength is found to be in reasonable agreement with the high density (HD) theory. The detector responsivity follows well the quantum efficiency predicted by scaling the free carrier absorption coefficient linearly with the doping concentration. All these comparisons are necessary to design and optimize GaAs HIWIP FIR detectors.

Bias effects in high performance GaAs homojunction far-infrared detectors

A high performance, bias tunable, p-GaAs homojunction interfacial workfunction internal photoemission far-infrared detector is demonstrated. A responsivity of 3.10±0.05 A/W, a quantum efficiency of 12.5%, and a detectivity D* of 5.9×1010 cmHz/W were obtained at 4.2 K for cutoff wavelengths from 80 to 100 μm. The bias dependences of the quantum efficiency, detectivity, and cutoff wavelength were measured and are well explained by the theoretical model. The effect of the layer number on detector performance and the uniformity of the detectors are discussed. A comparison with Ge:Ga photoconductive detectors suggests that similar or even better performance may be obtainable with a far-infrared detector.

Space-charge-limited conduction in Si n+–i–n+ homojunction far-infrared detectors

An analytic model is presented to describe the space-charge-limited (SCL) conduction in Si homojunction interfacial work-function internal photoemission far-infrared detectors. The basic detector unit is a thin n+–i–n+ structure, which is operated at low temperatures and characterized by an interfacial work function at the n+–i interface. The unique aspects of this case lead to simple analytic expressions for all variables of interest. The barrier shape and free-carrier concentration distribution in the i layer, and their dependence on the applied bias, i layer thickness, and compensating acceptor concentration, are calculated. The SCL current–voltage characteristic is also investigated as a function of i layer parameters. The results obtained are useful for the IR detector design and performance optimization.