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Study of Oxide Semiconductor ZnO with Deposition Temperatures Effect of on the Structural, Optical and Electrical Properties

This study demonstrates that depositing ZnO thin films via a spray pneumatic technique at 450°C yields optimal structural, optical, and electrical properties, including a maximum crystallite size of 15.19 nm, approximately 85% transparency, a band gap of 3.31 eV, and the lowest electrical resistivity of 0.064 Ω·cm.

Original authors: Abdelghani LAKEL, Said BENRAMACHE, Amira SBAIHI

Published 2026-07-03✓ Author reviewed ⓘ

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Abdelghani LAKEL, Said BENRAMACHE, Amira SBAIHI

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are a chef trying to bake the perfect batch of cookies. You have your ingredients (the dough), your pan (the glass substrate), and your oven. But the secret to getting the cookies to turn out crisp, golden, and perfectly shaped isn't just the recipe—it's the temperature of the oven.

This research paper is essentially a cooking log for a material called Zinc Oxide (ZnO). Instead of cookies, the "ingredients" are a chemical solution sprayed onto glass to create a very thin, invisible layer. The researchers wanted to find out: What happens to this layer if we bake it at different temperatures?

They tested three "oven settings": 350°C, 400°C, and 450°C. Here is what they found, broken down into simple concepts:

1. The Structure: Building a Better Neighborhood

Think of the atoms in the Zinc Oxide film like people in a neighborhood.

At lower temperatures (350°C): The neighborhood is a bit chaotic. The "houses" (crystals) are small and scattered.
At the highest temperature (450°C): The heat acts like a gentle organizer. The atoms have enough energy to move around and settle into a neat, orderly pattern.
The Result: The film baked at 450°C had the biggest, most organized "crystals" (about 15 nanometers wide). It was like the difference between a messy pile of LEGOs and a perfectly built castle. The researchers noticed a specific pattern called a "hexagonal wurtzite structure," which is just a fancy way of saying the atoms lined up in a very specific, efficient honeycomb-like shape.

2. The Light Show: How Clear is the Window?

Zinc Oxide is often used because it's transparent, like a window. The researchers shone light through their films to see how clear they were.

The Analogy: Imagine looking through a foggy window versus a clean, high-definition glass pane.
The Finding: The film baked at 450°C was the clearest. It let about 85% of visible light pass through.
Why? Because the "neighborhood" was so organized (as mentioned above), there were fewer gaps and defects to block or scatter the light. It was like the fog had cleared away.

3. The Energy Gap: The Size of the Jump

In the world of electronics, materials have an "energy gap." Think of this like a fence that electrons (the tiny particles that carry electricity) have to jump over to move from one side to the other.

The Finding: The height of this fence changed slightly depending on the temperature. At 450°C, the fence was just right (around 3.31 electron-volts).
The Disorder: They also measured something called "Urbach energy," which is basically a measure of how "messy" the material is. The 450°C film had the lowest messiness score, meaning the atoms were sitting very still and tidy, with very few defects.

4. The Electrical Flow: The Traffic Jam

Finally, they checked how easily electricity could flow through the film. This is measured by "resistivity" (how hard it is for electricity to pass).

The Twist: Usually, you want electricity to flow easily (low resistance). However, the paper reports a specific trend where the resistance changed as the temperature went up.
The Claim: The paper states that the film baked at 450°C had the lowest electrical resistivity (meaning electricity flowed most easily through it) with a value of 0.064.
- Note: The text in the "Results" section mentions a slight contradiction in numbers (saying it increased to 0.064), but the Conclusion explicitly states that the 450°C film had the "lowest electrical resistivity." We stick to the conclusion: The 450°C film was the best conductor among the three.

The Big Picture

The researchers used a "spray pneumatic technique," which is like using a very fine spray bottle to mist the chemical solution onto hot glass.

The Verdict:
If you want to make the best Zinc Oxide film for things like solar cells (which turn sunlight into electricity), 450°C is the magic temperature. At this heat, the material becomes:

More organized (bigger crystals).
Clearer (lets more light through).
Less messy (fewer defects).
Better at conducting electricity (according to the authors' final summary).

The paper doesn't claim to have built a working solar cell yet; it simply says, "We made the best possible raw material (the film) at this specific temperature, and here is the proof."

Technical Summary: Study of Oxide Semiconductor ZnO with Deposition Temperatures Effect on Structural, Optical and Electrical Properties

Problem Statement
Zinc oxide (ZnO) is a II–IV semiconductor recognized for its direct band gap of 3.37 eV, large exciton binding energy (60 meV), high transparency, and low electrical resistivity. While ZnO has established applications in optoelectronics, piezoelectric devices, solar cells, and LEDs, optimizing its fabrication parameters remains critical for performance. This study addresses the specific influence of deposition temperature on the structural, optical, and electrical properties of ZnO thin films, aiming to identify optimal conditions for producing high-quality films suitable for applications such as organic solar cells.

Methodology
The research utilized the spray pneumatic technique to deposit ZnO thin films onto glass substrates.

Precursor Solution: A 0.1 M solution of Zinc acetate dihydrate (Zn(CH3COO)2, 2H2O) was prepared in 100 ml of water. The solution was heated to 60 °C, and drops of HCl were added as a stabilizer until the solution became transparent.
Deposition Process: Films were sprayed onto heated glass substrates for a duration of 4 minutes. The study varied the substrate temperature across three levels: 350 °C, 400 °C, and 450 °C.
Characterization: The resulting films were analyzed using:
- X-ray Diffraction (XRD): (Bruker AXS-8D, $\lambda = 0.15406$ nm) to determine crystalline structure and crystallite size.
- UV-Visible Spectrophotometry: (Lambda 35, 300–900 nm) to measure optical transmission and calculate band gap energy.
- Four-Point Probe Method: To measure electrical resistivity.

Key Results

Structural Properties:
- All deposited films exhibited a polycrystalline hexagonal wurtzite structure.
- The films showed a strong preferred orientation along the (101) plane, which was the highest intensity peak compared to (100) and (002).
- Crystallite size increased significantly with temperature. The maximum crystallite size of 15.19 nm was achieved at 450 °C, compared to 9.96 nm at 350 °C.
- Higher temperatures (up to 450 °C) correlated with improved crystallinity and a reduction in lattice strain/defects.
Optical Properties:
- Transparency: The films demonstrated high transparency in the visible region. The film deposited at 450 °C exhibited the highest average transmission of approximately 85%.
- Band Gap: The optical band gap energy ( $E_g$ ) ranged from 3.28 eV to 3.31 eV. The value decreased at 400 °C before increasing at 450 °C, a trend attributed to the increase in crystallite size.
- Urbach Energy: The Urbach tail energy ( $E_u$ ), which indicates disorder and defects, reached a minimum of 0.328 eV at 450 °C. This suggests the film prepared at this temperature possesses the least disorder and fewest defects.
Electrical Properties:
- Electrical resistivity ( $\rho$ ) showed a non-linear relationship with temperature. It decreased from 0.014 to 0.012 $(\Omega \cdot cm)^{-1}$ as temperature rose from 350 to 400 °C.
- However, at 450 °C, the resistivity increased to 0.064 $(\Omega \cdot cm)^{-1}$ . The authors note this increase is explained by the concurrent increase in crystallite size.

Significance and Claims
The paper concludes that deposition temperature is a critical parameter in tailoring ZnO thin film properties. The study identifies 450 °C as the optimal temperature for achieving:

Maximum crystallite size (15.19 nm).
Highest optical transparency (~85%).
Minimum structural disorder (lowest Urbach energy).

While the electrical resistivity was highest at this temperature, the overall structural and optical improvements suggest that the 450 °C condition yields the highest quality films in terms of crystallinity and transparency, which are essential for optoelectronic applications like organic solar cells. The authors emphasize that the 450 °C film exhibits "less disorder with few defects," making it a superior candidate for device integration compared to films deposited at lower temperatures.