High-Temperature Optoelectronic Transport Behavior of n-TiO2 Nanoball–Stick/p-Lightly Boron-Doped Diamond Heterojunction

At a Glance

Metadata	Details
Publication Date	2025-01-10
Journal	Materials
Authors	Shunhao Ge, Dandan Sang, Changxing Li, Yarong Shi, Cong Wang
Institutions	Beijing University of Chemical Technology, Anhui East China Institute of Optoelectronic Technology (China)
Citations	1
Analysis	Full AI Review Included

Expert Analysis: High-Temperature Optoelectronic Transport Behavior of n-TiO₂ NBS/p-LBDD Heterojunction

Executive Summary

This research investigates the thermal stability and carrier transport mechanisms of a novel n-TiO₂ Nanoball-Stick (NBS) / p-Lightly Boron-Doped Diamond (LBDD) heterojunction, demonstrating its potential for high-temperature optoelectronic applications.

Material System & Synthesis: High-purity rutile-phase n-TiO₂ NBSs were successfully deposited on HFCVD-grown p-LBDD substrates using a hydrothermal method, confirming a high-density, uniform ball-stick structure.
Thermal Stability: The heterojunction exhibits excellent rectification characteristics and thermal stability across the tested range (Room Temperature (RT) to 200 °C).
Optimal Performance: Peak electrical performance was achieved at 150 °C, yielding the highest rectification ratio (16.39 ± 0.005) and the lowest turn-on voltage (0.4 V).
Backward Diode Transition: At 200 °C, the device transitions into a backward diode, characterized by a reverse rectification effect attributed to enhanced Fowler-Nordheim (F-N) tunneling of holes from the TiO₂ Valence Band (VB) to the LBDD Conduction Band (CB).
Carrier Transport Mechanism: Transport shifts from thermally excited diffusion and direct tunneling (low T) to F-N tunneling dominance (high T), driven by thermal excitation and Fermi level movement.
Optical Potential: Photoluminescence (PL) analysis shows emission peaks (402-456 nm) corresponding to the white-green light region (CIE coordinates: 0.2729, 0.3333), suitable for high-temperature LED applications.

Technical Specifications

Parameter	Value	Unit	Context
Optimal Operating Temperature	150	°C	Maximum rectification ratio achieved
Maximum Rectification Ratio	16.39 ± 0.005	N/A	Measured at ±8 V, 150 °C
Minimum Turn-On Voltage	0.4	V	Measured at 150 °C
Maximum Forward Current	0.295 ± 0.103	mA	Measured at 8 V, 150 °C
LBDD Carrier Concentration	2.3 x 10¹⁷	cm^-3	Hall effect measurement
LBDD Mobility	27.5	cm² V^-1 s^-1	Hall effect measurement
LBDD Resistivity	32.2	Ω cm	Hall effect measurement
TiO₂ Phase Dominance	Rutile	N/A	Confirmed by XRD (2θ = 27.46° for (110))
PL Emission Range	402, 410, 429, 456	nm	White-green light emission
CIE Chromaticity Coordinates	(0.2729, 0.3333)	N/A	Located in the white-green region
Ideal Factor (n) Range	16.43 to 19.23	N/A	Fitted across RT to 200 °C
TiO₂ Atomic Ratio (Ti:O)	~1:2	N/A	Confirmed by EDS analysis

Key Methodologies

The fabrication and characterization involved precise chemical synthesis and advanced electrical testing across a wide temperature range.

1. Substrate Preparation (p-LBDD Film)

Method: Hot Filament Chemical Vapor Deposition (HFCVD).
Substrate: p-type silicon wafers.
Gases: Hydrogen (H₂) and Methane (CH₄).
Boron Source: Liquid trimethyl borate ((CH₃O)₃B).

2. n-TiO₂ NBS Synthesis

Method: Hydrothermal synthesis.
Precursors: Reaction solution containing:
- Titanium trichloride (TiCl₃): 0.2 mol/L
- Sodium chloride (NaCl): 3.6 mol/L
Conditions: Sealed reactor, temperature maintained at 180 °C for 8 hours.
Post-Processing: Rinsed with ultrapure water, air-dried.

3. Device Fabrication and Contacting

Structure: n-TiO₂ NBS/p-LBDD heterojunction.
Anode/Cathode: Conductive copper wires connected via silver paste.
Interface Contact: TiO₂ NBSs contacted with the conductive side of transparent Indium Tin Oxide (ITO) glass, fixed with cyanoacrylate adhesive (ITO acts as a dielectric layer to prevent shorting at the LBDD bottom).
Ohmic Contacts: Confirmed linear I-V characteristics for Ag/ITO/Ag and Ag/LBDD/Ag contacts.

4. Characterization Techniques

Morphology & Composition: Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS).
Crystal Structure: X-ray Diffraction (XRD) (Bruker D8 ADVANCE).
Vibrational/Structural: Raman Spectroscopy (Renishaw inVia, 532 nm laser).
Optical Properties: Fluorescence Spectroscopy (FLS920, 365 nm excitation) and CIE Chromaticity Mapping.
Electrical Transport: I-V characteristics measured using a Keithley 2400 SourceMeter across temperatures from 25 °C to 200 °C.
Carrier Properties: Low-temperature high-resistance transport system (ET9110-HS) for Hall effect measurements on LBDD.

Commercial Applications

The combination of diamond’s exceptional thermal properties and TiO₂’s photoelectric efficiency makes this heterojunction highly valuable for specialized engineering fields.

Industry/Sector	Application/Product	Rationale
High-Temperature Power Electronics	Diodes, Rectifiers, Power Switches	Diamond’s high thermal conductivity ensures efficient heat dissipation, maintaining device stability and rectification performance up to 150 °C and potentially higher.
Aerospace and Automotive	Extreme Environment Sensors and Circuits	The inherent resistance of diamond to chemical and thermal degradation allows reliable operation in harsh, high-heat environments where silicon-based devices fail.
Solid-State Lighting (SSL)	White-Green Light-Emitting Diodes (LEDs)	The observed PL emission in the white-green region (402-456 nm) suggests direct application in specialized, thermally robust lighting systems.
High-Frequency Switching	Backward Diodes / Tunneling Devices	The controlled transition to a backward diode at 200 °C, driven by F-N tunneling, provides a physical principle for developing efficient high-temperature backward diodes used in high-frequency circuits.
Photovoltaics and Photocatalysis	UV Photodetectors, Water Splitting Catalysts	TiO₂’s large band gap and photoelectric conversion efficiency, coupled with the stability of the diamond substrate, enhance performance in UV detection and solar-driven chemical processes.

View Original Abstract

The n-TiO2 nanoballs-sticks (TiO2 NBSs) were successfully deposited on p-lightly boron-doped diamond (LBDD) substrates by the hydrothermal method. The temperature-dependent optoelectronic properties and carrier transport behavior of the n-TiO2 NBS/p-LBDD heterojunction were investigated. The photoluminescence (PL) of the heterojunction detected four distinct emission peaks at 402 nm, 410 nm, 429 nm, and 456 nm that have the potential to be applied in white-green light-emitting devices. The results of the I-V characteristic of the heterojunction exhibited excellent rectification characteristics and good thermal stability at all temperatures (RT-200 °C). The forward bias current increases gradually with the increase in external temperature. The temperature of 150 °C is ideal for the heterojunction to exhibit the best electrical performance with minimum turn-on voltage (0.4 V), the highest forward bias current (0.295 A ± 0.103 mA), and the largest rectification ratio (16.39 ± 0.005). It is transformed into a backward diode at 200 °C, which is attributed to a large number of carriers tunneling from the valence band (VB) of TiO2 to the conduction band (CB) of LBDD, forming an obvious reverse rectification effect. The carrier tunneling mechanism at different temperatures and voltages is analyzed in detail based on the schematic energy band structure and semiconductor theoretical model.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma18020303

References

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