JPH03138949A - Heterojunction bipolar transistor - Google Patents

Abstract

PURPOSE:To shorten running time in a base and to make it possible to manufacture a transistor simply at the good yield rate without deteriorating base resistance by providing a constitution wherein the potential in the conduction energy band of a second semiconductor material becomes higher than the conduction band of a third semiconductor material. CONSTITUTION:There is the discontinuance in a conduction band between the second semiconductor material and the third semiconductor material in a base layer (P<+> GaAs) 4a and a base layer (P<+> InGaAs) 4b. A staircase-shaped junction is provided so that the electron potential in the conduction band of the second semiconductor material is higher than that of the conduction band in the third semiconductor material. The fourth semiconductor material of a collector layer can be selectively etched with respect to the third semiconductor material. Since the new potential can be imparted by the staircase-shaped junction in this way, electrons can run through the base layers 4a and 4b at a high speed, and selective etching can be performed. The base layers 4a and 4b can be exposed by simple manufacturing steps, and the increase in external base resistance can be prevented. Thus, the heterojunction bipolar transistor characterized by high speed performance, easy manufacturing steps and high yield rate is obtained.

Description

[Detailed description of the invention] Industrial applications The present invention relates to heterojunction bipolar transistors.

Conventional technology In general, the cutoff frequency ft of a bipolar transistor can be expressed by the following formula.
τe is the charge time of the emitter depletion layer, τb is the carrier travel time in the base region, τC is the carrier travel time in the collector depletion layer, τcc is the collector depletion layer charging time, and the maximum oscillation frequency f-88 of the transistor is given by the following formula: Given also fs @X = ,? '[X CbcRb is the base resistor and Cbc is the base-collector capacitance a Recently, advances in manufacturing technology have made it possible to reduce parasitic capacitance and parasitic resistance, making it possible to obtain transistors that operate at high frequencies. In order to further improve the frequency characteristics, a major challenge is to reduce the short-edge base resistance of the carrier transit time in the base region. FIG. 3 shows an energy band diagram of the first conventional heterojunction bipolar transistor. A collector layer 35 made of low concentration n-type GaAs (nGaAs), a base layer 3 made of p-type GaAs (p"GaAs), and an n-type A1m, 5Gas, 〒As(nAl
Even in the structure in which the emitter layer 33 consisting of s, *Gae, vAs) is sequentially formed, the width of the base layer 34 is relatively long and 700 to 1000 layers in order to avoid an increase in base resistance and to facilitate the manufacturing process. In the operating state of the conventional heterojunction bipolar transistor, the emitter-base is a stepped junction, so hot electrons are injected from the emitter into the base. Electrons lose energy t, In order to shorten the travel time (τb) of the base, hot electrons from stepped junctions are used. Because the base width is long, the effect is small (t) Also, as the base width is shortened, the base resistance increases. Also, the manufacturing process However, the present invention has the disadvantage that it becomes difficult to conduct the process and reduces the yield.a The present invention effectively utilizes the hot electrons generated by the stepped junction between the base and emitter to shorten the base travel time and reduce the base resistance. The present invention has been made in view of the above points. An emitter (or collector) layer made of a first (or fourth) semiconductor material on a semi-insulating substrate, and a second (or third) semiconductor material and a third semiconductor material on this emitter (or collector) layer. In a heterojunction bipolar transistor having a base layer made of a (or fourth) semiconductor material, and a collector (or emitter) layer made of a fourth (or first) semiconductor material on the base layer, a second There is a band discontinuity in the conduction band between the semiconductor material and the third semiconductor material. 1. The potential strength of electrons in the conduction band of the second semiconductor material
The fourth (or first) semiconductor material is wet etched or dry etched with respect to the third (or second) semiconductor material. A heterojunction bipolar transistor characterized in that it can be selectively etched is obtained.The operation of the heterojunction bipolar transistor with the above-described base structure and semiconductor material is as follows. Compared to the shape junction,
The hot electrons injected from the emitter into the base, which has a new stepped junction in the base layer, travel through the base layer. Another stepped junction gives a new potential to the base. Don't make the width too short L
Electrons can travel through the base layer at high speeds, and the fourth (or first) semiconductor material of the collector (or emitter) layer can be etched selectively with respect to the third (or second) semiconductor material of the base layer. Arunohiro: A simple manufacturing process allows the base layer to be exposed without excessively etching the external base region, thereby preventing an increase in external base resistance. As described above, the present invention can provide a heterojunction bipolar transistor that has good high frequency characteristics and is easy to manufacture.
FIG. 1 is a cross-sectional view of a device for explaining the manufacturing process of an embodiment of the present invention.a A semi-insulating GaAs substrate 1 contains 3×10”/cm’ of n-type impurities by molecular beam epitaxy. 5000mm thick nGaAs emitter layer 2
, 2000 µm thick containing 5 x 10"/am" n-type impurities nAI@, 5Gas, tAsx transmitter layer 3, 4 x IO+"/Cf 400 µm thick containing 113 n-type impurities Base layer 4 made of p"GaAs, 200mm thick p-type 1ns, 2Gas, spring As (
pins, eGas, 5As) base layer 4. On this base layer 4b, there is a collector layer 5 made of nGaAs with a thickness of 5000 layers containing 5 x 10"/cm' n-type impurities. On this collector layer 6a, 5 layers are formed. x 10”/a
2000 nm thick nGa containing m” n-type impurities
A collector contact layer 6b made of As is sequentially laminated.
Although the interelement isolation layer 6 is formed by proton implantation, Ins, aGas, and S are etched using 5iC14 as an etching gas or by active ion etching (RIE)
When the GaAs layer formed on the As layer is etched and sown,
Although it has been reported that only the GaAs layer can be selectively removed by etching (Appl, Phy, Lett,
, 1987.51.2225) By using a similar method, after exposing the base layer 4b, protons are injected into the emitter layer 3 directly under the external base region to form a high resistance layer 3a. Electrons are injected from the emitter to the external base. Next, the emitter layer 2 is exposed and a collector electrode 7 made of 5000 layers of AuGe/Ni/Ti/Au is formed.
, emitter electrode 22. A collector top type heterojunction bipolar transistor is obtained by forming base electrodes 44 made of 2,000 ions of A and uZn, respectively. , *Ga
s, in sAS, GaAs and Ina, *Ga*, e
The lattice mismatch of As is about 1.5% force <, Ins
The film thicknesses of , tGas, and sAs are less than the critical film thickness of 200, so no dislocations occur and a good semiconductor junction is formed. Figure 2 shows the operating state of the heterojunction bipolar transistor of the first embodiment. shows the energy band structure of t'
The conduction band discontinuity △Ec and valence band discontinuity △Ev of oGaAS, Ins, and gGaseAs are △Ec, respectively.
J, t8eV, △Ev-0,03eV, p-type GaAs and p-type i1m, 2Gam in the base layer.
, sAs, although an ideal step-like junction can be obtained, the electrons injected from the emitter are nA1-, sGas,
The electrons heated by the 0.3 eV conduction band discontinuity in the emitter layer 3 made of As and the base layer 4a made of p-type GaAs are non-equilibrium between the 400 p-type GaAs and the short distance between them. Drive at high speed and at the end 0.1
In order to obtain energy again from the 8eV conduction band discontinuity, the base layer 4b made of p-type 1ns, tGas, and sAs can travel at high speed.
s, sAs is subjected to compressive stress and the degenerate valence band splits, so the effective mass of the light hole in the <3/2.3/2> band becomes smaller, and the p-type n@
Therefore, in this example, although the base width is 600 mm and thinner than the conventional example, the resistance of the base layer does not deteriorate, and selective etching reduces the resistance of the external base layer. Since the base layer can be exposed, an increase in the external base resistance due to the manufacturing process can be prevented. Effects of the Invention As described above, the present invention allows the base layer to be exposed to electrons without increasing the internal base resistance using a simple crystal structure. They can travel at high speed in a non-equilibrium state as hot electrons, and because the external base can be selectively exposed through a simple manufacturing process, high resistance of the external base can be prevented, and a heterojunction bipolar transistor with high yield can be realized. Seiya's easy manufacturing process and high yield can be expected to have a wide range of applications such as ultra-high-speed single devices and highly integrated devices.

[Brief explanation of the drawing]

FIG. 1 is an element cross-sectional diagram of a heterojunction bipolar transistor according to an embodiment of the present invention. FIG. 2 is an energy band diagram of an embodiment of the present invention. FIG. 3 is an energy band diagram of a conventional heterojunction bipolar transistor.

Claims (3)

[Claims] (1) An emitter (or collector) layer made of a first (or fourth) semiconductor material on a semi-insulating substrate, and a second (or third) semiconductor material on this emitter (or collector) layer. A heterojunction bipolar transistor having a base layer made of a third (or fourth) semiconductor material, and a collector (or emitter) layer made of a fourth (or first) semiconductor material on the base layer; There is a conduction band discontinuity between the second semiconductor material and the third semiconductor material, such that the conduction band energy band potential of the second semiconductor material is higher with respect to the conduction band of the third semiconductor material. A heterojunction bipolar transistor characterized by: (2) An emitter (or collector) layer made of a first (or fourth) semiconductor material on a semi-insulating substrate, and a second (or third) semiconductor material on this emitter (or collector) layer. A heterojunction bipolar transistor having a base layer made of a third (or fourth) semiconductor material, and a collector (or emitter) layer made of a fourth (or first) semiconductor material on the base layer; 4 (or 1st
) can be selectively etched with respect to the second (or third) semiconductor material by wet or dry etching. (3) an emitter layer made of AlGaAs on a semi-insulating substrate; a first base layer made of GaAs on this emitter layer; a second base layer made of InGaAs on this first base layer; Claim 1 or 2 comprises a collector layer made of GaAs (or AlGaAs) on a base layer of
Heterojunction bipolar transistor as described in .