Progress on photovoltaic AlGaN photodiodes for solar-blind ultraviolet photodetection

Xu Liu; Shengjun Zhou

doi:10.3788/COL202220.112501

Journals >Chinese Optics Letters >Volume 20 >Issue 11 >Page 112501 > Article

Chinese Optics Letters
Vol. 20, Issue 11, 112501 (2022)

Progress on photovoltaic AlGaN photodiodes for solar-blind ultraviolet photodetection

Xu Liu and Shengjun Zhou^*

Author Affiliations

Center for Photonics and Semiconductors, School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, China

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DOI: 10.3788/COL202220.112501 Cite this Article Set citation alerts

Xu Liu, Shengjun Zhou. Progress on photovoltaic AlGaN photodiodes for solar-blind ultraviolet photodetection[J]. Chinese Optics Letters, 2022, 20(11): 112501 Copy Citation Text

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Cross-section SEM images of (a) stripe-shaped PSS, (b) AlN/PSS template, and (c) AlGaN epitaxial film grown on AlN/PSS template. Reproduced with permission[16]. Copyright 2013, Elsevier.

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(a) Schematic diagram of the DUV LED grown on AlN/Gr/NPSS. (b) EL spectra of the DUV-LEDs with and without the Gr interlayer. Cross-sectional SEM images of AlN films on NPSS (c) without and (d) with the Gr interlayer. AlN has realized complete coalescence below a thickness of 1 µm in (d), which is less than half of the thickness (about 2.4 µm) on bare NPSS in (c). Reproduced with permission[17]. Copyright 2019, American Institute of Physics Publishing.

Fig. 2. (a) Schematic diagram of the DUV LED grown on AlN/Gr/NPSS. (b) EL spectra of the DUV-LEDs with and without the Gr interlayer. Cross-sectional SEM images of AlN films on NPSS (c) without and (d) with the Gr interlayer. AlN has realized complete coalescence below a thickness of 1 µm in (d), which is less than half of the thickness (about 2.4 µm) on bare NPSS in (c). Reproduced with permission^[17]. Copyright 2019, American Institute of Physics Publishing.

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Fig. 3. AFM images of the NLs deposited at (a) 950°C, (b) 1050°C, and (c) 1150°C after being recrystallized at 1250°C. AFM images of AlN epitaxial films on NLs deposited at (d) 850°C, (e) 950°C, (f) 1050°C, (g) 1150°C, and (h) 1250°C. Reproduced with permission^[65]. Copyright 2014, Elsevier.

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Fig. 4. Cross-section TEM images of AlN/FSS without AlN SL in the (a) g = (0002) direction and (b) g =

(11 \bar{2} 0)

direction. Cross-section TEM images of AlN/FSS without AlN SL in the (c) g = (0002) direction and (d) g =

(11 \bar{2} 0)

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Fig. 5. (a) Illustration of samples with four types of distinct AlN layer structures. (b) Dislocation density of samples A–D. (c) FWHM and individual rocking curves of samples A–D. (d) Schematic illustration of the growth mechanism and dislocation annihilation for sample C. Reproduced with permission^[82]. Copyright 2016, Elsevier.

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Fig. 6. Cross-section TEM images of (a) AlN/FSS and (b) AlN/NPSS in the g =

(11 \bar{2} 0)

direction. FWHM for AlN/FSS and AlN/NPSS at different stages: (c) (002) reflection peak and (f) (102) reflection peak. (d) Enlarged TEM image of the void in AlN/FSS. (e) Schematic diagrams of dislocation behavior in AlN epitaxial film. Reproduced with permission^[85]. Copyright 2020, Elsevier.

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Fig. 7. (a) Schematic diagram of AlGaN-heterostructure MSM SBPD. (b) Responsivity of the MSM SBPD with and without photonic crystals. (c) Reflectivity and transmissivity of the AlGaN MSM SBPD with and without photonic crystals. (d) I-V characteristics of AlGaN MSM SBPD. Reproduced with permission^[97]. Copyright 2021, American Institute of Physics Publishing.

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Fig. 8. (a) Device structure of the AlGaN MQWs SBPD. (b) I-V characteristic of Al_0.64Ga_0.36N/Al_0.34Ga_0.66N SBPD in the dark. (c) Responsivity spectrum of AlGaN MQWs SBPD at -0.5 V. Reproduced with permission^[89]. Copyright 2017, Institute of Physics.

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Fig. 9. Schematic diagrams of (a) Al_0.15Ga_0.85N/Al_0.15Ga_0.85N SAM-APD SBPD and (b) dual-periodic DBR. (c) Reflectivity of single- and dual-periodic DBR. (d) Responsivity of the SAM-APD SBPDs with single-/dual-periodic and without DBR at 10 V reverse bias. The single-periodic DBR is composed of 25 pairs of AlN/Al_0.55Ga_0.45N (A/B). Reproduced with permission^[133]. Copyright 2017, Institute of Physics. (e) Cross-section TEM image of the DBR with 20-pair AlGaN/AlInN/AlInGaN layers. (f) Measured and simulated reflectivity of the DBR with 20-pair AlGaN/AlInN/AlInGaN layers. Reproduced with permission^[134]. Copyright 2016, Springer Nature Publishing Group.

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Fig. 10. (a) Schematic and physical images of AlGaN-based p-i-n SBPD. (b) I-V curve and the corresponding current density of the device. (c) Spectral responsivity of AlGaN-based p-i-n SBPD under different bias. The inset shows the responsivity plot in semi-log scale. (d) The corresponding EQE in semi-log scale. The inset shows the variation trend of EQE with applied bias. Reproduced with permission^[149]. Copyright 2020, Elsevier.

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Fig. 11. (a) Schematic structure of HDT-modified AlGaN SBPD. (b) Top-view photograph of HDT-modified AlGaN SBPD. Responsivity of AlGaN SBPD (c) without and (d) with HDT modification at various bias. (e) Dark current of AlGaN SBPD with and without HDT modification. (f) Electrical breakdown characteristics of the AlGaN SBPD with and without HDT modification. Reproduced with permission^[151]. Copyright 2021, Optical Society of America.

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Fig. 12. (a) Schematic illustration of Pd-decorated Al_0.4Ga_0.6N MSM SBPD. (b) I-V characteristics of Al_0.4Ga_0.6N MSM SBPD with and without Pd NPs in the dark and in the 280/500 nm irradiation. The inset shows the top-view image of the Al_0.4Ga_0.6N MSM SBPD. (c) PDCR-V characteristics for the incident wavelength of 500 and 280 nm for the Al_0.4Ga_0.6N MSM SBPD with and without Pd NPs. (d) Responsivity spectra of Al_0.4Ga_0.6N solar-blind PD with and without Pd NPs at -10 V with incident wavelength from 220 to 300 nm. The inset shows the variation in a broad spectral range from 220 to 500 nm. (e) Responsivity spectra of Al_0.4Ga_0.6N solar-blind PD with and without Pd NPs in the 280 nm irradiation at different voltages. (f) The plot of responsivity with voltage at 500, 280, and 220 nm for Pd-decorated Al_0.4Ga_0.6N MSM SBPD. Reproduced with permission^[155]. Copyright 2022, Institute of Physics.

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Fig. 14. Schematic illustrations of (a) Pt/AlGaN nanostructures on Si and (b) self-powered Pt/AlGaN PEC-SBPDs. (c)–(e) TEM images and STEM-EDS elemental mapping of Pt/AlGaN-50 nanostructures. Photocurrent densities of AlGaN nanostructures (f) at UV radiation of 254 and 365 nm and (g) at different incident 254 nm solar-blind light intensities. (h) Photocurrent densities of Pt/AlGaN-50 nanostructures at different incident light power intensities. (i) Photocurrent densities and ratios of Pt/AlGaN nanostructures with various Pt loading amounts. (j) Response and recovery time of Pt/AlGaN PEC-SBPDs with different Pt loading amounts. (k) Photocurrent densities and responsivities of Pt/AlGaN-50 nanostructures at different incident light power intensities. Reproduced with permission^[157]. Copyright 2020, American Chemical Society.

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Fig. 15. Schematic diagrams of (a) MPC-DUV LED, (b) carrier recombination and generation in MPC-DUV LED, and (c) photon recycle, gain, and output process in the MPC-DUV LED. Reproduced with permission^[182]. Copyright 2019, Elsevier.

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Template	Thickness (μm)	Nucleation Layer	Defect Density^a ( ${cm}^{- 2}$ )	Highlights	Ref.
AlN/MPSS	10.6	LT-AlN	Total: $3 \times 10^{8}$	1. PALE-induced^b and ELOG-induced voids are both introduced in the AlN epilayer during growth.	[29]
			S: $5.9 \times 10^{7}$	2. These voids facilitate the defect termination and strain release in the AlN epilayer.
			E: $2.3 \times 10^{8}$
AlN/FSS	6	LT-AlN	TD: $< 10^{8}$	1. The nanoscale ELOG is achieved on the AlN rods/FSS template.	[30]
			S: $3.5 \times 10^{8}$	2. The advantage of the nanoscale ELOG is that even the dislocations in the center of the rod do not have a long distance to bend into the voids between the rods.
			E: None	3. TDs bend at slight angles due to the nano-scaled air gaps and the rod diameters by nano-ELOG.
AlN/MPSS	2.54	–	Total: $1 \times 10^{8}$	1. The effect of PSS on reducing defect density is investigated.	[31]
			EP: $2.3 \times 10^{5}$	2. AlN layers with gradient V/III ratio and period AlN superlattice layers (SLs) are introduced into the AlN epilayer to reduce defect density.
			EP: $2.3 \times 10^{5}$	3. The behaviors of defect termination are exhibited quantitatively.
AlN/NPSS	3.25	LT-AlN	TD: $1 \times 10^{9}$	The intrinsic mechanism of bending dislocations by employing AlN SLs with period high/low V/III ratio is revealed in Fig. 4.	[32]
AlN/FSS	2	Sputtered AlN LT-AlN	EP: $4.8 \times 10^{7}$	1. The effect of AlN NL thickness on optical transmittance, strain state, surface morphology, and TD density of AlN epilayer is investigated.	[14]
				2. The AlN epilayer with O-doped sputtered AlN NL has the highest optical transmittance.
				3. The AlN epilayer with undoped sputtered AlN NL has the smoothest surface morphology and lowest TD density.
AlN/MPSS	8–10	Sputtered AlN	S: $2.6 \times 10^{7}$	1. Misaligned AlN growth could be overcome by selecting an appropriate growth temperature.	[33]
AlN/MPSS	8–10	Sputtered AlN	E: $1.8 \times 10^{9}$	2. Optimizing the PSS geometries is important for rapid coalescence of the AlN epilayer. In this paper, the grown AlN deviating from the c-axis on sapphire near r-plane sidewalls has less influence on the coalescence of AlN grown from the c-axis-oriented sapphire plane, compared to near n-plane sidewalls.	[33]
AlN/NPSS	1	Sputtered AlN	TD: $6 \times 10^{8}$	1. The growth temperature can exert a strong impact on the crystalline quality of AlN epitaxial films by influencing the diffusion length of adatoms and lateral growth rate.	[34]
AlN/NPSS	1	Sputtered AlN	TD: $6 \times 10^{8}$	2. The flat AlN films are realized on AlN/NPSS with a total coalescence at a growth temperature of 1300°C.	[34]
AlN/FSS	85	–	–	1. Self-separation of AlN epitaxial film is achieved by the formation of voids at the AlN/sapphire interface during the HVPE growth at 1450°C.	[35]
AlN/FSS	85	–	–	2. Voids are formed by decomposition of sapphire during the HVPE of the AlN epilayer, and their size is dominated by the heating time.	[35]

Table 1. Summary of the Reported AlN/Sapphire Template

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Absorption Layer	Device	$I_{dark}$ (A)	$R$ (mA/W)	Wavelength (nm)	$D^{*}$ ( $cm {Hz}^{1 / 2} W^{- 1}$ )	$G$	EQE	Ref.
${Al}_{0.38} {Ga}_{0.62} N$	Schottky	$4 \times 10^{- 12} @ - 20 V$	90	274	$2.6 \times 10^{12}$	–	42%	[86]
AlGaN/GaN	Schottky	$\sim 1 \times 10^{- 12} @ - 20 V$	44	274	–	–	21%	[87]
${Al}_{0.75} {Ga}_{0.25} N$	Schottky	$\sim 1 \times 10^{- 13} @ - 100 V$	530	229	$1.64 \times 10^{12}$	–	–	[88]
${Al}_{0.4} {Ga}_{0.6} N$	Schottky	$1.2 \times 10^{- 12} @ - 10 V$	41	260	$7.0 \times 10^{14}$	–	20%	[36]
AlGaN MQWs	p-n	$1 \times 10^{- 13} @ - 0.5 V$	100	250	–	–	50%	[89]
${Al}_{0.4} {Ga}_{0.6} N$	p-i-n	$\sim 1 \times 10^{- 13} @ - 10 V$	79	280	$5.3 \times 10^{13}$	–	35%	[90]
${Al}_{0.45} {Ga}_{0.55} N$	p-i-n	$3 \times 10^{- 15} @ - 6 V$	110	283	$4.9 \times 10^{14}$	–	43%	[91]
$AlN / {Al}_{0.08} {Ga}_{0.92} N$	p-i-n	$5.3 \times 10^{- 16} @ \sim 0 V$	62	247	$4.5 \times 10^{13}$	–	30%	[92]
${Al}_{0.45} {Ga}_{0.55} N$	p-i-n	$5 \times 10^{- 6} @ - 5 V$	136	282	–	–	72%	[93]
${Al}_{0.4} {Ga}_{0.6} N$	p-i-n	$5 \times 10^{- 15} @ - 10 V$	93	280	$7.5 \times 10^{14}$	–	42%	[94]
${Al}_{0.4} {Ga}_{0.6} N$	p-i-n	$1.6 \times 10^{- 12} @ - 10 V$	211	289	$6.1 \times 10^{14}$	–	92%	[95]
${Al}_{0.4} {Ga}_{0.6} N$	MSM	$10^{- 15} @ 20 V$	140	272	–	–	64%	[96]
${Al}_{0.42} {Ga}_{0.58} N$	MSM	$2 \times 10^{- 12} @ 20 V$	–	285	–	–	–	[97]
${Al}_{0.6} {Ga}_{0.4} N$	MSM	$\sim 10^{- 15} @ \sim 0 V$	2750	250	–	–	–	[98]
AlGaN/Al NPs	MSM	$\sim 10^{- 13} @ 0 V$	288	288	–	–	–	[99]
${Al}_{0.4} {Ga}_{0.6} N$	APD	$3.3 \times 10^{- 12} @ - 10 V$	79.8	270	–	$> 2500 @ - 65 V$	37%	[100]
${Al}_{0.38} {Ga}_{0.62} N$	APD	$3 \times 10^{- 13} @ - 20 V$	132	281	–	$3000 @ - 91 V$	58.2%	[101]
${Al}_{0.4} {Ga}_{0.6} N$	APD	$10^{- 12} @ - 100 V$	98	262	–	$4000 @ - 177 V$	46%	[102]
${Al}_{0.4} {Ga}_{0.6} N$	APD	$1.5 \times 10^{- 10} @ - 60 V$	150	280	–	$12, 000 @ - 84 V$	50%	[103]
${Al}_{0.2} {Ga}_{0.8} N / {Al}_{0.45} {Ga}_{0.55} N$	APD	$\sim 10^{- 11} @ - 20 V$	–	275	–	$55, 000 @ - 109 V$	98.5%	[104]
AlGaN/GaN	APD	$5 \times 10^{- 10} @ - 86 V$	–	275	–	$10, 000 @ - 92 V$	–	[105]

Table 2. Summary of Performance Parameters on the Reported AlGaN SBPDs

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Absorption Layer	Enhanced Technique	$I_{dark}$ (A)	$R$ (A/W)	Wavelength (nm)	Ref.
${Al}_{0.6} {Ga}_{0.4} N / {Al}_{0.5} {Ga}_{0.5} N$	Polarization	$10^{- 11} @ 5 V$	$10^{6}$	280	[146]
${Al}_{0.6} {Ga}_{0.4} N / {Al}_{0.45} {Ga}_{0.55} N$	Polarization	$\sim 3 \times 10^{- 12} @ - 2 V$	3.1	280	[147]
${Al}_{0.1} {Ga}_{0.9} N / GaN$	Polarization	$\sim 1 \times 10^{- 13} @ 0 V$	12.5	266	[148]
Al_xGa_1−xN	Polarization	$\sim 10^{- 11} @ 0 V$	0.204	274	[149]
AlN	Surface modification	$\sim 10^{- 12} @ - 2 V$	$6 \times 10^{- 4}$	200	[150]
${Al}_{0.6} {Ga}_{0.4} N$	Surface modification	$\sim 10^{- 14} @ \sim - 2.5 V$	7.6	250	[151]
${Al}_{0.6} {Ga}_{0.4} N$	Surface modification	$\sim 10^{- 15} @ 0 V$	2.75	250	[98]
${Al}_{0.5} {Ga}_{0.5} N / {Al}_{0.4} {Ga}_{0.6} N$	Surface modification	$1.47 \times 10^{- 11} @ \sim 5 V$	$\sim 100$	260	[152]
AlGaN	LSPR	$\sim 10^{- 13} @ 0 V$	0.288	288	[99]
${Al}_{0.54} {Ga}_{0.46} N$	LSPR	$\sim 10^{- 13} @ 0 V$	2.34	269	[153]
${Al}_{0.4} {Ga}_{0.6} N$	LSPR	$\sim 2 \times 10^{- 13} @ 20 V$	0.3	265	[154]
${Al}_{0.4} {Ga}_{0.6} N$	LSPR	$10^{- 14} @ \sim 0 V$	2.7	280	[155]
Ru/AlGaN	PCE	–	0.0488	254	[156]
Pt/AlGaN	PCE	–	0.045	254	[157]

Table 3. Summary of Performance Parameters on the Enhanced Techniques of Reported AlGaN SBPDs

Xu Liu, Shengjun Zhou. Progress on photovoltaic AlGaN photodiodes for solar-blind ultraviolet photodetection[J]. Chinese Optics Letters, 2022, 20(11): 112501

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