MATERIALS—n- AND p-TYPEThe characte

MATERIALS—
n- AND p-TYPE
The characteristics of semiconductor materials can be altered significantly by the ad- dition of certain impurity atoms into the relatively pure semiconductor material. These impurities, although only added to perhaps 1 part in 10 million, can alter the band structure sufficiently to totally change the electrical properties of the material.
A semiconductor material that has been subjected to the doping process is called an extrinsic material.
There are two extrinsic materials of immeasurable importance to semiconductor device fabrication: n-type and p-type. Each will be described in some detail in the following paragraphs.

n-Type Material
Both the n- and p-type materials are formed by adding a predetermined number of impurity atoms into a germanium or silicon base. The n-type is created by introduc- ing those impurity elements that have five valence electrons (pentavalent), such as an- timony, arsenic, and phosphorus. The effect of such impurity elements is indicated in


















Figure 1.9 Antimony impurity in n-type material.



Fig. 1.9 (using antimony as the impurity in a silicon base). Note that the four cova- lent bonds are still present. There is, however, an additional fifth electron due to the impurity atom, which is unassociated with any particular covalent bond. This re- maining electron, loosely bound to its parent (antimony) atom, is relatively free to move within the newly formed n-type material. Since the inserted impurity atom has donated a relatively “free” electron to the structure:
Diffused impurities with five valence electrons are called donor atoms.
It is important to realize that even though a large number of “free” carriers have been established in the n-type material, it is still electrically neutral since ideally the number of positively charged protons in the nuclei is still equal to the number of “free” and orbiting negatively charged electrons in the structure.
The effect of this doping process on the relative conductivity can best be described through the use of the energy-band diagram of Fig. 1.10. Note that a discrete energy level (called the donor level) appears in the forbidden band with an Eg significantly less than that of the intrinsic material. Those “free” electrons due to the added im- purity sit at this energy level and have less difficulty absorbing a sufficient measure of thermal energy to move into the conduction band at room temperature. The result is that at room temperature, there are a large number of carriers (electrons) in the conduction level and the conductivity of the material increases significantly. At room temperature in an intrinsic Si material there is about one free electron for every 1012 atoms (1 to 109 for Ge). If our dosage level were 1 in 10 million (107), the ratio
(1012/107 = 105) would indicate that the carrier concentration has increased by a ra- tio of 100,000:1.


Energy






Eg as before

Conduction band





Valence band



Eg = 0.05 eV (Si), 0.01 eV (Ge)
Donor energy level





Figure 1.10 Effect of donor impurities on the energy band structure.


Type Material
The p-type material is formed by doping a pure germanium or silicon crystal with impurity atoms having three valence electrons. The elements most frequently used for this purpose are boron, gallium, and indium. The effect of one of these elements, boron, on a base of silicon is indicated in Fig. 1.11.

















Figure 1.11 Boron impurity in
p-type material.


Note that there is now an insufficient number of electrons to complete the cova- lent bonds of the newly formed lattice. The resulting vacancy is called a hole and is represented by a small circle or positive sign due to the absence of a negative charge. Since the resulting vacancy will readily accept a “free” electron:
The diffused impurities with three valence electrons are called acceptor atoms.
The resulting p-type material is electrically neutral, for the same reasons described for the n-type material.

Electron versus Hole Flow
The effect of the hole on conduction is shown in Fig. 1.12. If a valence electron ac- quires sufficient kinetic energy to break its covalent bond and fills the void created by a hole, then a vacancy, or hole, will be created in the covalent bond that released the electron. There is, therefore, a transfer of holes to the left and electrons to the right, as shown in Fig. 1.12. The direction to be used in this text is that of conven- tional flow, which is indicated by the direction of hole flow.















Figure 1.12 Electron versus hole flow.


Hạt tải điện đa số và thiểu số

Kết quả (Việt) 1:

VẬT LIỆU —KIỂU n và pCác đặc tính của vật liệu bán dẫn có thể được thay đổi đáng kể bởi dition quảng cáo nhất định nguyên tử tạp chất vào vật liệu bán dẫn tương đối tinh khiết. Các tạp chất, mặc dù chỉ được thêm vào để có lẽ 1 phần trong 10 triệu, có thể thay đổi cấu trúc ban nhạc đầy đủ để hoàn toàn thay đổi các thuộc tính điện của vật liệu.Một vật liệu bán dẫn đã được chịu các quá trình doping được gọi là một vật liệu bên ngoài.Có hai các vật liệu bên ngoài có tầm quan trọng bao la để chế tạo thiết bị bán dẫn: n-loại và kiểu p. Mỗi sẽ được mô tả trong một số chi tiết trong các đoạn sau đây.n-loại vật liệuCả hai tài liệu kiểu n và p được hình thành bằng cách thêm một số định trước các tạp chất nguyên tử vào một gecmani hoặc silic cơ sở. N-loại được tạo ra bởi gi-ing những yếu tố tạp chất có năm điện tử của hóa trị (pentavalent), chẳng hạn như một timony, asen, và phốt pho. Ảnh hưởng của các yếu tố tạp chất được chỉ định trongCon số 1.9 Antimony tạp chất trong n-loại vật liệu.Hình 1.9 (sử dụng antimon như tạp chất trong một cơ sở silic). Lưu ý rằng bốn cova-vay trái phiếu được vẫn còn hiện diện. Có đó, Tuy nhiên, một electron thứ năm bổ sung do nguyên tử tạp chất, là chưa kết hợp với bất kỳ trái phiếu liên cụ thể. Này điện tử re-maining, lỏng lẻo bị ràng buộc với nguyên tử phụ huynh (antimon), là tương đối tự do để di chuyển trong các tài liệu n-kiểu mới được thành lập. Kể từ khi các nguyên tử được chèn vào tạp chất đã đóng góp một điện tử tương đối "miễn phí" cho cấu trúc:Diffused impurities with five valence electrons are called donor atoms.It is important to realize that even though a large number of “free” carriers have been established in the n-type material, it is still electrically neutral since ideally the number of positively charged protons in the nuclei is still equal to the number of “free” and orbiting negatively charged electrons in the structure.The effect of this doping process on the relative conductivity can best be described through the use of the energy-band diagram of Fig. 1.10. Note that a discrete energy level (called the donor level) appears in the forbidden band with an Eg significantly less than that of the intrinsic material. Those “free” electrons due to the added im- purity sit at this energy level and have less difficulty absorbing a sufficient measure of thermal energy to move into the conduction band at room temperature. The result is that at room temperature, there are a large number of carriers (electrons) in the conduction level and the conductivity of the material increases significantly. At room temperature in an intrinsic Si material there is about one free electron for every 1012 atoms (1 to 109 for Ge). If our dosage level were 1 in 10 million (107), the ratio(1012/107 = 105) would indicate that the carrier concentration has increased by a ra- tio of 100,000:1.EnergyEg as beforeConduction bandValence bandEg = 0.05 eV (Si), 0.01 eV (Ge)Donor energy levelFigure 1.10 Effect of donor impurities on the energy band structure.Type MaterialThe p-type material is formed by doping a pure germanium or silicon crystal with impurity atoms having three valence electrons. The elements most frequently used for this purpose are boron, gallium, and indium. The effect of one of these elements, boron, on a base of silicon is indicated in Fig. 1.11.Figure 1.11 Boron impurity inp-type material.Note that there is now an insufficient number of electrons to complete the cova- lent bonds of the newly formed lattice. The resulting vacancy is called a hole and is represented by a small circle or positive sign due to the absence of a negative charge. Since the resulting vacancy will readily accept a “free” electron:The diffused impurities with three valence electrons are called acceptor atoms.The resulting p-type material is electrically neutral, for the same reasons described for the n-type material.Electron versus Hole FlowThe effect of the hole on conduction is shown in Fig. 1.12. If a valence electron ac- quires sufficient kinetic energy to break its covalent bond and fills the void created by a hole, then a vacancy, or hole, will be created in the covalent bond that released the electron. There is, therefore, a transfer of holes to the left and electrons to the right, as shown in Fig. 1.12. The direction to be used in this text is that of conven- tional flow, which is indicated by the direction of hole flow.Con số 1,12 các điện tử so với lỗ chảy.Hạt tải điện đa số và thiểu số