One-sided Junction Research Articles

InP/InGaAs Uni-Traveling-Carrier Photodiode (UTC-PD) With Improved EM Field Response

In this article, a unique structure of InP/InGaAs uni-traveling-carrier photodiode (UTC-PD) is proposed. Compared with the one-sided junction photodiode, the UTC-PD has the advantages of a simpler epitaxial layer structure while maintaining the characteristics of high bandwidth and high output power loss profile. Simulated results show that a large built-in electric field can be generated under illumination, which aids UTC carrier velocity. The merits of the new structure are compared to a standard UTC-PD photodiode in terms of improved electric field and carrier concentration response. It is demonstrated that the photogeneration and light absorption of UTC-PDs are improved by incorporating a step-like internal texture of cones and dots profile in the photo absorption layer. The simulated device shows a peak electrical 3-dB bandwidth of 65 GHz at a low light intensity and reverse bias voltage. The performance characteristics of 1-D and 2-D UTC-PD simulations, including internal electric field distribution, energy band diagram, carrier concentration, and power loss distribution, are carefully studied. A theoretical discussion of the working principle and key performance characteristics of a UTC-PD enhanced by heterojunction design is reported. The entire physical environment is modeled and simulated through the finite element method (FEM) using commercial software. The proposed photodiode structure configuration is designed and optimized for photodetectors for high RF frequencies at different light intensities. To the best of our knowledge, the obtained bandwidth and electric field response is the fastest among those reported for other various higher wavelength photodiodes.

Design and Simulation of Highly Efficient One-Sided Short PIN Diode Silicon Heterojunction Solar Cell

Performance of highly efficient one-sided short PIN diode heterojunction solar cell model is studied using AFORS-HET simulation software. Here, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> -type crystalline silicon is used as an absorber layer, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -type amorphous silicon as emitter layer, and a thin intrinsic amorphous silicon (i-a-Si:H) layer is sandwiched in between, which acts as a passivation layer. The diode model concept has been introduced mainly to lower the reverse saturation current by appropriate selection of the cell parameters. Short diode reduces recombination phenomenon in the short quasi-neutral region (n-a-Si:H in this article), and one-sided junction allows the maximum amount of light absorption in the absorber layer (p-c-Si in this article). The one-sided junction nature has been confirmed by capacitance–voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C–V</i> ) analysis. Further thickness variation of layers and role of the carrier concentration of n-a-Si layer on various parameters, such as short-circuit current density ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> ), open-circuit voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> ), and fill factor (FF) have also been studied. The structure has exhibited an open circuit voltage of 0.714 V, fill factor 0.80, and maximum efficiency of 24.2%. Further, experimental validation is also established by comparing the theoretical results with the fabricated NIP structure.

Determining limitations of capacitance-voltage measurements of built-in voltage as an alternative to surface photovoltage for a-Si:H/c-Si heterojunctions

Strong band bending within crystalline silicon is important for improving carrier selectivity in the contact regions of silicon heterojunction solar cells. In this work, we compare the use of capacitance-voltage as an alternative to the surface photovoltage method for probing the built-in voltage associated with crystalline silicon band bending. The surface photovoltage technique is incapable of measuring structures with non-transparent contacts, while the capacitance-voltage technique shows saturation at high built-in voltages due to the formation of an inversion layer. The shift in built-in voltage and effect on open circuit voltage are demonstrated for variation across a range of amorphous Si p-doping levels. These experimental results are supported by simulation work, confirming the underlying band structure and carrier concentrations of photovoltaic Si heterojunctions and clarifying the limitations of capacitance measurements at high built-in voltages. Errors arising in capacitance-voltage measurements of these structures are explained and linked to deviations from the Mott-Schottky model approximations of a one-sided junction in full depletion.

InGaAs/InP evanescently coupled one-sided junction waveguide photodiode design

An evanescently coupled one-sided junction waveguide photodiode (EC-OSJ-WGPD) is proposed and investigated numerically. The one-sided junction photodiode has a simple structure, while the characteristics of high speed and high output power are maintained. The designed EC-OSJ-WGPD with an absorption layer thickness of 350 nm achieves a bandwidth of 44.5 GHz and responsivity of 0.98 A/W. Comprehensive analyses of the EC-OSJ-WGPD are presented including photogeneration rate, internal optical power distribution, energy band diagram, internal electric field, photocurrent, and 3-dB bandwidth.

Design of high speed InGaAs/InP one-sided junction photodiodes with low junction capacitance

A high speed InGaAs/InP one-sided junction photodiode (OSJ-PD) with low junction capacitance is presented and investigated for the first time. Compared with the well known uni-traveling carrier photodiode (UTC-PD), the OSJ-PD has the advantages of simpler epitaxial layer structure and lower junction capacitance, while maintaining the characteristics of high speed and high output power. The OSJ-PD is studied by simulation. The performance characteristics of OSJ-PD including internal electric field distribution, energy band diagram, frequency response, photocurrent and junction capacitance, are carefully studied.

Design of modified InGaAs/InP one-sided junction photodiodes with improved response at high light intensity.

A modified InGaAs/InP one-sided junction photodiode (MOSJ-PD) is presented for the first time. The MOSJ-PD is proposed from the one-sided junction photodiode by inserting a cliff layer into the absorption layer. Compared to the modified uni-traveling carrier photodiode, the MOSJ-PD has the advantages of simpler epitaxial layer structure and lower junction capacitance. In the MOSJ-PD, the space charge effect at high light intensity can be suppressed. Thus, both 3-dB bandwidth and output current can be improved simultaneously. The performance characteristics of the MOSJ-PD, including energy band diagram, internal electric field, frequency response, photocurrent, and responsivity, are carefully studied.

Approximate values of the multiplication coefficient in one-sided abrupt junctions

In this paper, a simple method is proposed for calculating the multiplication coefficient M in abrupt one-sided junctions near the breakdown. The empirical law of S.L. Miller [1]: 1− 1 M = V V B n V B breakdown voltage is taken as the first term of a series expansion near the breakdown of the function 1−(1/ M), the value of the exponent n being linked to the physical parameters of the junction and to the type (electron or hole) of the incident carrier. The method is developed for several different materials: Ge, GaAs, GaP, Si using well established data for ionization rates. The values of the multiplication coefficient given by the approximation is compared to the computed exact values obtained by the calculation of the ionization integrals. We found that the approximation is correct with an accuracy of ±10% for a large variation of the ratio V/ V B .

High injection in narrow uniform p-n junctions: A second-approximation model

The classical first-approximation high-injection theory in narrow uniform p-n junctions is based on two restrictive assumptions: negligible majority carrier current in the less-doped region (the theory applies to one-sided junctions only) and quasi-neutrality outside the space-charge layer. It has been shown in the literature that, in order to remove both assumptions, numerical integration methods are required. A second-approximation model is proposed in this paper, in which only the first of the two assumptions is removed. This model approaches the accuracy of the exact numerical solution, while still retaining all the advantages of the classical theory, i.e., the availability of analytical solutions and a better physical understanding of the high-injection phenomenon. Furthermore, the proposed model is not restricted to one-sided junctions only.

Interpretation of capacitance vs. voltage measurements of p- n junctions

In profiling impurity distributions by use of differential capacitance measurements, it has been customary to interpret d( 1 C 2 )/ dV as proportional to the inverse of impurity concentration at the edge of the depletion region for a one-sided junction. In a recent paper, based on numerical calculations, Kennedy, Murley and Kleinfelder (KMK) observed that this interpretation is incorrect and that d( 1 C 2 )/ dV yields the zero-bias majority carrier distribution. In the present paper, again based on numerical calculations, we show that while the KMK interpretation is approximately correct in that the apparent doping concentration found by applying the C- V relation is an excellent approximation to the zero-bias majority carrier concentration, the two are not exactly equal. This imposes limitations on applying the correction described by Kennedy and O'Brien to obtain the actual impurity concentration from the apparent doping concentration.