Solar-blind Avalanche Photodiodes Research Articles

Improved performance of AlGaN solar-blind avalanche photodiodes with dual multiplication layers

Improved performance of AlGaN solar-blind avalanche photodiodes with dual multiplication layers

AlGaN solar-blind ultraviolet avalanche photodiodes with a p-graded AlxGa1-xN layer and high/low Al-content AlGaN multiplication layer

We design a back-illuminated p–i–n–i–n separate absorption and multiplication (SAM) AlGaN solar-blind avalanche photodiode (APD) with a low Al-content p-graded AlxGa1-xN layer and a high/low Al-content AlGaN multiplication layer. Simultaneously, an III-nitride AlN/Al0.64Ga0.36 N distributed Bragg reflector (DBR) structure is inserted to improve the solar-blind photoresponse for the designed APD. The simulation results show that the designed APD exhibits enhanced optoelectronic characteristics compared to the conventional APD, which is attributed to the higher holes impact ionization coefficient and generated polarization electric field in the same direction as the applied bias field of the designed APD. The designed APD exhibits significant enhanced avalanche gain and reduced avalanche breakdown voltage compared with the conventional APD.

High gain, large area, and solar blind avalanche photodiodes based on Al-rich AlGaN grown on AlN substrates

We demonstrate large area (25 000 μm2) Al-rich AlGaN-based avalanche photodiodes (APDs) grown on single crystal AlN substrates operating with differential (the difference in photocurrent and dark current) signal gain of 100 000 at 90 pW (<1 μW cm−2) illumination with very low dark currents <0.1 pA at room temperature under ambient light. The high gain in large area AlGaN APDs is attributed to a high breakdown voltage at 340 V, corresponding to very high breakdown fields ∼9 MV cm−1 as a consequence of low threading and screw dislocation densities < 103 cm−2. The maximum charge collection efficiency of 30% was determined at 255 nm, corresponding to the bandgap of Al0.65Ga0.35N, with a response of 0.06 A/W. No response was detected for λ > 280 nm, establishing solar blindness of the device.

Back-illuminated AlGaN heterostructure solar-blind avalanche photodiodes with one-dimensional photonic crystal filter.

AlGaN heterostructure solar-blind avalanche photodiodes (APDs) were fabricated on a double-polished AlN/sapphire template based on a separate absorption and multiplication (SAM) back-illuminated configuration. By employing AlGaN heterostructures with different Al compositions across the entire device, the SAM APD achieved an avalanche gain of over 1×105 at an operated reverse bias of 92 V and a low dark current of 0.5 nA at the onset point of breakdown. These excellent performances were attributed to the acceleration of holes by the polarization electric field with the same direction as the reverse bias and higher impact ionization coefficient of the low-Al-content Al0.2Ga0.8N in the multiplication region. However, the Al0.2Ga0.8N layer produced a photocurrent response in the out of the solar-blind band. To retain the solar-blind detecting characteristic, a periodic Si3N4/SiO2 photonic crystal was deposited on the back of the AlN/sapphire template as an optical filter. This significantly improved the solar-blind characteristic of the device.

Separate Absorption and Multiplication AlGaN Solar-Blind Avalanche Photodiodes With High-low-Doped and Heterostructured Charge Layer

In this work, an AlGaN solar-blind ultraviolet separate-absorption-and-multiplication avalanche photodiode is presented, where the charge layer has a high-low-doping (HLD) profile and a lower Al content. It was shown by numerical simulations that the HLD not only improved the transport efficiency of holes crossing the charge layer, but also enhanced the electric fields in the multiplication region. Moreover, a lower Al-content charge layer may induce a polarization effect to further increase the electric fields in the multiplication layers, promoting the impact ionization in the multiplication region and decreasing the avalanche breakdown voltage. The HLD and heterostructure employed in the charge layer can also improve the photoresponse by enhancing the electric field and inducing the upward valence-band bending.

Hybrid Light Emitters and UV Solar-Blind Avalanche Photodiodes based on III-Nitride Semiconductors.

In the last two decades, remarkable progress has been achieved in the field of optoelectronic devices based on III-nitride semiconductors. In terms of photonics applications in the visible-UV spectral range, III-nitrides are one of the most promising materials. For instance, emerging gallium nitride (GaN)-based micro-light-emitting diode (LED) technology for high-resolution display, and UV photo-detection for environmental monitoring, health, and medical applications. In this work, hybrid micro/nano-LEDs with integration of II-VI quantum dots by means of lithography and nano-imprinting patterning techniques are demonstrated, and high-performance red/green/blue and white emissions are achieved. Consequently, plasmonic nanolasers are designed and fabricated using a metal-oxide-semiconductor structure, where strong surface plasmon polariton coupling leads to the efficient lasing with a low excitation threshold from the visible to UV tunable spectral range. Furthermore, performance-improved AlGaN UV solar-blind avalanche photodiodes (APDs) with a separate absorption and multiplication structure by polarization engineering are reported. These APDs deliver a record-high avalanche gain of up to 1.6 × 105 . These newest advances in nano/micro-LEDs, nanolasers, and APDs can shed light on the emerging capabilities of III-nitride in cutting-edge applications.

AlGaN Solar-Blind Avalanche Photodiodes With p-Type Hexagonal Boron Nitride

To improve the performances of AlGaN solar-blind avalanche photodiodes (APDs), we propose a separate absorption and multiplication AlGaN APD with a p-hBN layer. The simulated results show that the p-hBN/AlGaN APD significantly decreases the breakdown voltage almost by 23% in comparison with the conventional AlGaN APD due to the use of p-hBN, which has a wider bandgap, a higher p-type doping efficiency, and a smaller spontaneous polarization. Moreover, the designed APD keeps an intrinsic solar-blind characteristic even at large reverse bias because the h-BN is completely transparent in the long wavelength direction outside the solar-blind region. The result also confirms that the p-hBN/AlGaN APD has the lower Flicker and impact ionization noise at low and medium frequency under breakdown voltage.

Polarization and p-type doping effects on photoresponse of separate absorption and multiplication AlGaN solar-blind avalanche photodiodes

The photoresponse characteristics of separate absorption and multiplication (SAM) AlGaN solar-blind avalanche photodiodes (APDs) were investigated in detail. The p-i-n-i-n avalanche photodiodes were examined using the newly designed model of avalanche photodiodes in AlGaN. The research results showed that the dark current density was about 3.51 × 10−8 A/cm2, the light current density was 5.86 × 10−5 A/cm2 under near-zero bias, and the avalanche breakdown occurred at about 135.0 V under reverse bias, which were all consistent with the experimental data. To investigate the effects influencing the photoresponse characteristics of the APDs, their photo responsivity spectra under different biases were simulated. The APD featured a window region over the wavelength range from 260 to 280 nm with a high rejection ratio on the short-wavelength side. Meanwhile, the dependence of APD responsivity on the polarization charge revealed that the negative polarization charges strongly affected the responsivity. Increased negative polarization charges at the Al0.4Ga0.6N/Al0.6Ga0.4N interface markedly lowered the responsivity, whereas charges of the same polarity at the GaN/Al0.4Ga0.6N interface enhanced the responsivity. Furthermore, the dependence of responsivity on p-type doping was analyzed by comparison with the effects of negative polarization charges on the conduction band of the APDs. Finally, the inversion layer models are used to interpret the effects of these on the APD responsivity. This research is useful for exploring polarization and p-type doping effects in SAM AlGaN structures and realization of high responsivity solar-blind APDs.

An Improved Design for Solar-Blind AlGaN Avalanche Photodiodes

To enhance the impact ionization coefficient of holes, we proposed an improved solar-blind AlGaN avalanche photodiode (APD) structure by using a low-Al-composition AlGaN multiplication layer and a filter based on periodic photonic crystal together with a composition graded interlayer between separate absorption and multiplication regions. The simulation results show that the improved APD presents a lower breakdown voltage and dark current, and a higher optical gain when compared to its conventional counterpart. Further, we found that the composition graded interlayer can modify profitably energy-band profile of heterostructure interfaces besides adjusting the electric field distribution, which is beneficial to the injection of holes from the absorption region to multiplication region. Therefore, we optimized the doping concentration and thickness of the interlayer, and analyzed the effects of these parameters on the APD performances.

Fine Control of the Electric Field Distribution in the Heterostructure Multiplication Region of AlGaN Avalanche Photodiodes

To enhance avalanche ionization, we designed a new separate absorption and multiplication AlGaN solar-blind avalanche photodiode (APD) by replacing the conventional AlGaN homogeneous multiplication region with a high/low Al content AlGaN heterostructure layer. The calculated results showed that the improved APD with the Al0.3 Ga0.7N/Al0.45Ga0.55N heterogeneous multiplication region exhibits 51% higher gain than that of the conventional APD, benefiting from the six times higher hole ionization coefficient of Al 0.3Ga0.7N, compared to that of Al0.45Ga0.55N. Furthermore, we inserted an intermediate n-type AlGaN charge layer into the heterogeneous multiplication region to obtain superior performance by finely controlling the electric field distribution. The dependence of breakdown voltage and multiplication gain on the Al content, doping concentration, and thickness of the charge layer is studied in detail to get the optimal structure. Meanwhile, the solar-blind characteristic is also taken into account when optimizing the APD structure.

Trap-assisted tunneling in AlGaN avalanche photodiodes

We fabricated AlGaN solar-blind avalanche photodiodes (APDs) that were based on separate absorption and multiplication (SAM) structures. It was determined experimentally that the dark current in these APDs is rapidly enhanced when the applied voltage exceeds 52 V. Theoretical analyses demonstrated that the breakdown voltage at 52 V is mainly related to the local trap-assisted tunneling effect. Because the dark current is mainly dependent on the trap states as a result of modification of the lifetimes of the electrons in the trap states, the tunneling processes can be modulated effectively by tuning the trap energy level, the trap density, and the tunnel mass.

AlGaN solar-blind avalanche photodiodes with AlInN/AlGaN distributed Bragg reflectors

AlGaN solar-blind avalanche photodiodes (APDs) with AlInN/AlGaN distributed Bragg reflectors (DBRs) operated at lower avalanche breakdown voltage are numerically demonstrated. The p-type AlGaN layer and the multiplicative layer with low Al composition are introduced to construct the polarization-induced electric field, which can significantly reduce the avalanche breakdown voltage of the APDs. Calculated results exhibit that the avalanche breakdown voltage of the designed APDs decrease by 13% compared with the conventional device structure. Simultaneously, an improved solar-blind spectral responsivity is achieved due to the inserted AlInN/AlGaN DBRs.

High-performance AlGaN-based solar-blind avalanche photodiodes with dual-periodic III–nitride distributed Bragg reflectors

Separate absorption and multiplication AlGaN solar-blind avalanche photodiodes with dual-periodic III–nitride distributed Bragg reflectors (DBRs) are numerically demonstrated. The designed devices exhibit an improved solar-blind characteristic with a maximum spectral responsivity of 0.184 A/W at λ = 284 nm owing to the optimized optical properties of the dual-periodic III–nitride DBRs. Compared with their conventional counterparts, an increased multiplication gain and a reduced breakdown voltage are achieved by using p-type Al0.15Ga0.85N layers with a lower Al content and multiplication layers. These improvements are attributed to the high p-doping efficiency and large hole ionization coefficient.

An improved design for AlGaN solar-blind avalanche photodiodes with enhanced avalanche ionization**Project supported by the State Key Project of Research and Development Plan, China (Grant No. 2016YFB0400903), the National Natural Science Foundation of China (Grant Nos. 61634002, 61274075, and 61474060), the Key Project of Jiangsu Province, China (Grant No. BE2016174), the Anhui University Natural Science Research Project, China (Grant No.

To enhance the avalanche ionization, we designed a new separate absorption and multiplication AlGaN solar-blind avalanche photodiode (APD) by using a high/low-Al-content AlGaN heterostructure as the multiplication region instead of the conventional AlGaN homogeneous layer. The calculated results show that the designed APD with Al0.3Ga0.7N/Al0.45Ga0.55N heterostructure multiplication region exhibits a 60% higher gain than the conventional APD and a smaller avalanche breakdown voltage due to the use of the low-Al-content Al0.3Ga0.7N which has about a six times higher hole ionization coefficient than the high-Al-content Al0.45Ga0.55N. Meanwhile, the designed APD still remains a good solar-blind characteristic by introducing a quarter-wave AlGaN/AlN distributed Bragg reflectors structure at the bottom of the device.

High-Gain N-Face AlGaN Solar-Blind Avalanche Photodiodes Using a Heterostructure as Separate Absorption and Multiplication Regions**Supported by the State Key Project of Research and Development Plan of China under Grant No 2016YFB0400903, the National Natural Science Foundation of China under Grant Nos 61634002, 61274075 and 61474060, the Key Project of Jiangsu Province under Grant No BE2016174, the Anhui University Natural Science

It is well known that -nitride semiconductors can generate the magnitude of MV/cm polarization electric field which is comparable with their ionization electric fields. To take full advantage of the polarization electric field, we design an N-face AlGaN solar-blind avalanche photodiode (APD) with an Al0.45Ga0.55N/Al0.3Ga0.7N heterostructure as separate absorption and multiplication (SAM) regions. The simulation results show that the N-face APDs are more beneficial to improving the avalanche gain and reducing the avalanche breakdown voltage compared with the Ga-face APDs due to the effect of the polarization electric field. Furthermore, the Al0.45Ga0.55N/Al0.3Ga0.7N heterostructure SAM regions used in APDs instead of homogeneous Al0.45Ga0.55N SAM structure can increase significantly avalanche gain because of the increased hole ionization coefficient by using the relatively low Al-content AlGaN in the multiplication region. Meanwhile, a quarter-wave AlGaN/AlN distributed Bragg reflector structure at the bottom of the device is designed to remain a solar-blind characteristic of the heterostructure SAM-APDs.

All AlGaN epitaxial structure solar-blind avalanche photodiodes with high efficiency and high gain

Solar-blind avalanche photodiodes were fabricated with an all AlGaN-based epitaxial structure on sapphire by metal–organic chemical vapor deposition. The devices demonstrate a maximum responsivity of 114.1 mA/W at 278 nm and zero bias, corresponding to an external quantum efficiency (EQE) of 52.7%. The EQE improves to 64.8% under a bias of −10 V. Avalanche gain higher than 2 × 104 was obtained at a bias of −140 V. The high performance is attributed to the all AlGaN-based p–i–n structure comprised of undoped and Si-doped n-type Al0.4Ga0.6N on a high quality AlN layer and highly conductive p-type AlGaN grown with In-surfactant-assisted Mg-delta doping.

Solar blind avalanche photodetector based on the cation exchange growth of β-Ga2O3/SnO2 bilayer heterostructure thin film

Solar blind photodetectors have shown a paramount encouragement owing to their promising applications in the fields of ultraviolet (UV) astronomy, fire alarms, missile warning, environmental studies, biological/chemical analysis and short range communication security. Due to the weak solar blind signal, there is a real need to develop solar blind avalanche photodiode (APD) with high internal avalanche gain to compete with the commercial Si APDs and photomultiplier tubes. Herein, we report the development of APD based on the growth of two wide band gap metal oxides operating within the solar blind region of the UV-spectrum (200–280nm). It was found that the growth of β-Ga2O3 on SnO2 thin film via cation exchange mechanism results in the development of a solar blind photodetector with ultrahigh sensitivity, high spectral selectivity, very fast response, high stability and high signal to noise ratio. The high external quantum efficiency of the APD developed was assigned to the avalanche multiplication effect.

Study on AlGaN P-I-N-I-N solar-blind avalanche photodiodes with Al0.45Ga0.55N multiplication layer

This paper presents the design for a heterojunction AlGaN solar-blind avalanche photodiode (APD) with improved noise performance. Increasing the Al composition of AlGaN in the multiplication layer from 0.40 to 0.45 was calculated to significantly reduce the excess noise factor of this heterojunction APD. The polarization electric field induced in the multiplication layer had the same direction as the applied reverse bias field, which helped lower the avalanche breakdown voltage. The calculated results demonstrated that the apparent spike in the electric field intensity at the i-Al0.4Ga0.6N/n-Al0.5Ga0.5N interface can be effectively suppressed by inserting a grading n-AlGaN layer, which helps reduce the dark current.

Back-Illuminated GaN/AlGaN Solar-Blind Avalanche Photodiodes

The separate absorption and multiplication (SAM) GaN/AlGaN solar-blind avalanche photodiodes (APDs) integrated with the specific design of 1-D dual-periodic photonic crystal on the back of the sapphire substrate are investigated numerically. The calculated results show that the proposed APDs can increase significantly the avalanche gain compared with the conventional SAM AlGaN solar-blind APDs using GaN instead of AlGaN as the multiplication layer. The enhanced performance can be explained by the larger hole ionization coefficient in the multiplication layer, the higher hole injection efficiency, and the reduced total dark current in this APDs. Meanwhile, the cutoff wavelength of 282 nm is achieved due to the optical filter effect of 1-D dual-periodic photonic crystal.

Significant Performance Improvement in AlGaN Solar-Blind Avalanche Photodiodes by Exploiting the Built-In Polarization Electric Field

We present improved AlGaN solar-blind avalanche photodiodes (APDs) with a separate absorption and multiplication (SAM) structure by introducing a polarization electric field with the same direction as reverse bias field in the multiplication region. This polarization electric field can be realized by reducing the Al composition of the p-AlGaN layer in a conventional p-i-n-i-n SAM-APD structure. After employing a reduced-Al-composition p-AlGaN instead of the commonly used p-AlGaN, the polarization enhanced APD exhibits a markedly lower avalanche breakdown voltage and a near two times higher avalanche gain up to 2.1 × 10 4 compared with its conventional counterpart. In addition, X-ray diffraction and transmission electron microscopy results show that a moderate reduction of Al composition in the p-AlGaN layer does not degrade the crystalline quality of the polarization enhanced APD structure resulted from lattice mismatch, which guarantees the polarization enhanced effect.