diff --git a/electronics/builtin_voltage.py b/electronics/builtin_voltage.py
new file mode 100644
index 000000000..38fde4524
--- /dev/null
+++ b/electronics/builtin_voltage.py
@@ -0,0 +1,67 @@
+from math import log
+
+from scipy.constants import Boltzmann, physical_constants
+
+T = 300  # TEMPERATURE (unit = K)
+
+
+def builtin_voltage(
+    donor_conc: float,  # donor concentration
+    acceptor_conc: float,  # acceptor concentration
+    intrinsic_conc: float,  # intrinsic concentration
+) -> float:
+    """
+    This function can calculate the Builtin Voltage of a pn junction diode.
+    This is calculated from the given three values.
+    Examples -
+    >>> builtin_voltage(donor_conc=1e17, acceptor_conc=1e17, intrinsic_conc=1e10)
+    0.833370010652644
+    >>> builtin_voltage(donor_conc=0, acceptor_conc=1600, intrinsic_conc=200)
+    Traceback (most recent call last):
+      ...
+    ValueError: Donor concentration should be positive
+    >>> builtin_voltage(donor_conc=1000, acceptor_conc=0, intrinsic_conc=1200)
+    Traceback (most recent call last):
+      ...
+    ValueError: Acceptor concentration should be positive
+    >>> builtin_voltage(donor_conc=1000, acceptor_conc=1000, intrinsic_conc=0)
+    Traceback (most recent call last):
+      ...
+    ValueError: Intrinsic concentration should be positive
+    >>> builtin_voltage(donor_conc=1000, acceptor_conc=3000, intrinsic_conc=2000)
+    Traceback (most recent call last):
+      ...
+    ValueError: Donor concentration should be greater than intrinsic concentration
+    >>> builtin_voltage(donor_conc=3000, acceptor_conc=1000, intrinsic_conc=2000)
+    Traceback (most recent call last):
+      ...
+    ValueError: Acceptor concentration should be greater than intrinsic concentration
+    """
+
+    if donor_conc <= 0:
+        raise ValueError("Donor concentration should be positive")
+    elif acceptor_conc <= 0:
+        raise ValueError("Acceptor concentration should be positive")
+    elif intrinsic_conc <= 0:
+        raise ValueError("Intrinsic concentration should be positive")
+    elif donor_conc <= intrinsic_conc:
+        raise ValueError(
+            "Donor concentration should be greater than intrinsic concentration"
+        )
+    elif acceptor_conc <= intrinsic_conc:
+        raise ValueError(
+            "Acceptor concentration should be greater than intrinsic concentration"
+        )
+    else:
+        return (
+            Boltzmann
+            * T
+            * log((donor_conc * acceptor_conc) / intrinsic_conc**2)
+            / physical_constants["electron volt"][0]
+        )
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
diff --git a/hashes/elf.py b/hashes/elf.py
index 87fe339da..e4bfcec22 100644
--- a/hashes/elf.py
+++ b/hashes/elf.py
@@ -2,19 +2,17 @@ def elf_hash(data: str) -> int:
     """
     Implementation of ElfHash Algorithm, a variant of PJW hash function.
 
-    Returns:
-        [int] -- [32 bit binary int]
     >>> elf_hash('lorem ipsum')
     253956621
     """
-    hash = x = 0
+    hash_ = x = 0
     for letter in data:
-        hash = (hash << 4) + ord(letter)
-        x = hash & 0xF0000000
+        hash_ = (hash_ << 4) + ord(letter)
+        x = hash_ & 0xF0000000
         if x != 0:
-            hash ^= x >> 24
-        hash &= ~x
-    return hash
+            hash_ ^= x >> 24
+        hash_ &= ~x
+    return hash_
 
 
 if __name__ == "__main__":