10.1
Yarı İletkenin Temelleri
İzole edilmiş atomlar, Bohr modeli tarafından iyi tanımlanan ayrık enerji seviyelerine sahiptir. Ve bir hidrojen atomundaki bir elektronun enerjisini…
Katılar, farklı elektronik konfigürasyonlara ve enerji seviyelerine sahip atomlardan oluşur.
İki özdeş izole atom birbirine yaklaştırıldığında, etkileşimleri her bir enerji seviyesinin iki farklı seviyeye bölünmesine neden olur.
Bu bölünme, bir atomdaki iki elektronun aynı anda aynı enerji durumunu işgal edemeyeceğini belirten Pauli dışlama ilkesinin bir sonucudur.
Birkaç atom bir katı oluşturmak için bir araya getirilirse, enerji seviyeleri sürekli bir bant oluşturmak için bölünür. Denge atomlar arası aralıkta, bant değerlik bandına ve iletim bandına ayrılır.
Mutlak sıfır sıcaklıkta, değerlik bandı elektronlarla dolu enerji seviyelerini içerir.
Değerlik bandının üzerinde, boş enerji seviyelerini içeren iletim bandı bulunur.
Bu iki bant arasındaki enerji boşluğuna bant boşluğu denir. Değerlik bandının üst kısmı ile iletim bandının alt kısmı arasındaki enerji farkını temsil eder.
View the full transcript and gain access to JoVE Core videos
Q1: Why do energy levels split when atoms are brought together in a solid?
Energy levels split due to the Pauli exclusion principle, which states that no two electrons can occupy the same energy state simultaneously. When atoms approach each other, their electron orbitals overlap, forcing electrons into different energy states. As more atoms combine, splitting becomes so fine that discrete levels merge into continuous energy bands.
Q2: What is the difference between the valence band and conduction band?
The valence band contains energy levels filled with electrons at absolute zero temperature, while the conduction band sits above it with vacant energy levels. The energy gap between these two bands is called the band gap. This gap determines how easily electrons can be excited into the conduction band for electrical conduction.
Q3: How does the band gap affect semiconductor electrical properties?
The band gap size is crucial because it determines how easily electrons transition into the conduction band. In semiconductors, the band gap is small enough that thermal energy or light can excite electrons across the gap, resulting in electrical conduction. This property distinguishes semiconductors from insulators and conductors.
Q4: What role do valence electrons play in silicon's electrical properties?
Silicon has four valence electrons in its 3s and 3p subshells that determine its chemical and electrical properties. These electrons form bands when silicon atoms create a crystal lattice. The valence band contains 4N states and the conduction band contains 4N states, where N is the number of silicon atoms.
Q5: How many energy states exist in semiconductor bands?
In semiconductors like silicon, the valence band and conduction band each contain 4N energy states, where N represents the number of atoms in the crystal. This large number of states creates the continuous band structure. At equilibrium interatomic spacing, these bands form from overlapping 3s and 3p subshells.
Q6: Why do inner electrons in silicon not contribute to electrical conduction?
Silicon's inner 10 electrons occupy deep-lying energy levels that remain filled and do not participate in bonding or conduction. Only the four valence electrons in the 3s and 3p subshells contribute to the material's electrical properties. These valence electrons form the bands responsible for carrier generation and recombination in semiconductor devices.
Q7: What happens to discrete energy levels as more atoms combine in a solid?
As more atoms combine, the number of discrete energy levels increases exponentially, and the splitting between them becomes so fine that individual levels merge into continuous energy bands. At equilibrium interatomic distance, these bands separate into the valence band and conduction band. This band formation is fundamental to understanding semiconductor behavior.