<p>This study presents the fabrication and characterization of a silicon-based heterojunction photodiode featuring a rare-earth orthoborate interlayer, aimed at enhancing high-sensitivity photodetection. The orthoborate compound was synthesized by the solid-state reaction method and confirmed to have high phase purity and thermal stability up to 800&#xa0;&#xa0;C. Structural and spectroscopic analyses (PXRD, FTIR, and SEM/EDS) verified a uniform microstructure and well-defined borate framework. The device showed clear rectifying behavior with very low dark current, indicating good junction quality and effective carrier separation. Illumination induced systematic changes in ideality factor, barrier height, and saturation current, consistent with photon-assisted transport. The photodiode achieved high photosensitivity and stable responsivity across different illumination levels, particularly under low-light conditions. Under 100 <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(mW\,cm^{ - 1}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>m</mi> <mi>W</mi> <mspace width="0.166667em" /> <mi>c</mi> <msup> <mi>m</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation> illumination, the responsivity reached <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(0.43{ }A/W\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>0.43</mn> <mrow /> <mi>A</mi> <mo stretchy="false">/</mo> <mi>W</mi> </mrow> </math></EquationSource> </InlineEquation> and specific detectivity exceeded <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(2.5{ } \times 10^{10} {\text{ Jones}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>2.5</mn> <mrow /> <mo>×</mo> <msup> <mn>10</mn> <mn>10</mn> </msup> <mrow> <mspace width="0.333333em" /> <mtext>Jones</mtext> </mrow> </mrow> </math></EquationSource> </InlineEquation>. Time-resolved measurements demonstrated rapid and repeatable switching with no hysteresis, confirming operational stability. These results demonstrate that the <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>A</mi> <mi>l</mi> <mo stretchy="false">/</mo> <mi>N</mi> <mi>a</mi> <mi>S</mi> <mi>r</mi> <mi>L</mi> <mi>a</mi> <msub> <mfenced close=")" open="("> <mrow> <mi>B</mi> <msub> <mi>O</mi> <mn>3</mn> </msub> </mrow> </mfenced> <mn>2</mn> </msub> <mo stretchy="false">/</mo> <mi>n</mi> <mo>-</mo> <mi>S</mi> <mi>i</mi> </mrow> </math></EquationSource> </InlineEquation> heterojunction is a promising platform for sensitive and stable photodetection in optoelectronic applications.</p>