JP2662039B2 - Bipolar transistor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a bipolar transistor used for switching a large current.

2. Description of the Related Art One of the problems of bipolar transistors, particularly power bipolar transistors, is thermal runaway. The thermal runaway that occurs in a bipolar transistor results from the fact that the base-emitter barrier potential V _BE decreases with increasing temperature, thereby increasing the collector current and further increasing the bipolar transistor temperature due to the increase in the collector current. Positive feedback destruction. This thermal runaway is particularly likely to occur in a large-area element for power. As a method of preventing thermal runaway, a resistor with a positive temperature coefficient of resistance is formed in the emitter region, and the decrease in V _BE caused by temperature rise is
There is a method of compensating for the voltage by an incremental change expressed by the product of the increase in the resistance value of the resistor and the emitter current. Conventionally, this resistor has been formed by evaporating a metal such as Ni / Cr to a thickness of several hundreds of meters.

Hereinafter, a conventional bipolar transistor structure will be described with reference to the drawings.

FIG. 2 is a perspective view of a conventional bipolar transistor. In FIG. 2, 1 is a collector layer, 2 is a base layer, 3 is an emitter layer, and 4 is a resistor formed by vapor deposition of Ni / Cr. 5 is a collector electrode, 6 is a base electrode, and 7 is an emitter electrode.

When the temperature is T, V _BE , the resistance value of the Ni / Cr ballast resistor re,
Between the emitter current Ie There is a relationship, To become Conditions are required.

From this relationship, it is understood that thermal runaway can be prevented by setting an appropriate resistance value re for a certain emitter current Ie.

However, in the structure having a resistor made of a metal thin film as described above, since the film thickness is extremely thin, it is difficult to control the film thickness, and the reproducibility of the resistance value of the resistor is extremely low. It had the disadvantage of being bad.

Means for Solving the Problems In view of the above drawbacks, the bipolar transistor of the present invention has a collector layer and an emitter layer formed on both sides of a base layer, and has the same conductive layer as the emitter layer on the emitter layer. A resistor layer having a lower impurity concentration than that of the emitter layer and a composition different from that of the emitter layer, and having the same conductivity type as the resistor layer on the resistor layer; A contact layer having a higher impurity concentration is formed, and an emitter electrode is formed on the contact layer.

Operation With this configuration, since the temperature coefficient of the resistance value of the semiconductor layer formed between the emitter layer and the emitter electrode is positive, the decrease in V _BE due to the temperature rise causes It can be compensated for by the voltage increment represented by the product of the increase in the resistance value and the current flowing through the semiconductor layer,
This prevents thermal runaway of the bipolar transistor. Further, this semiconductor layer can be formed with good controllability by using an epitaxial growth technique, and a bipolar transistor can be manufactured with good reproducibility by one epitaxial growth.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a bipolar transistor according to one embodiment of the present invention.

In FIG. 1, reference numeral 11 denotes an n-type GaAs layer having an impurity concentration of 1 × 10 ¹⁶ / cm ³ and a thickness of 0.3 μm as a collector layer, and reference numeral 12 denotes an impurity concentration of 1 × 10 ¹⁸ / cm ^{3 as} a base layer. 0.1 μm thick
P-type GaAs layer 13 has an emitter concentration of 5 ×
An n-type Al _0.3 Ga _0.7 As layer having a thickness of 10 ¹⁷ / cm ³ and a thickness of 0.25 μm. An impurity concentration 14 serving as a resistor is 1 × 10 ¹⁶ / cm ³ and a thickness of 0.4 μm.
N-type GaAs layer, 15 and 16 are high-concentration n-type GaAs layers for taking ohmic electrodes, and 17 is AuGe to be
A / Au film, 18 is a Ti / Pt / Au film serving as a base electrode, 19 is an AuGe / Au film serving as an emitter electrode, and 20 is an undoped GaAs substrate.

Hereinafter, a method for manufacturing a bipolar transistor according to one embodiment of the present invention will be described.

The above-mentioned semiconductor layer is first formed on an undoped GaAs substrate 20 by using MBE to form a high concentration GaAs layer 16, a collector layer 11, a base layer 12, an emitter layer 13, a resistor layer 14, and a high concentration GaAs.
Layer 15 is continuously epitaxially grown.

Next, the emitter region is covered with a photoresist, and the high-concentration GaAs layer 15 and the GaAs layer 14 serving as a resistor are selectively etched by RIE using CCl ₂ H ₂ / H ₂ gas. Is used to selectively etch the Al _0.3 Ga _0.7 As layer 13 to expose the base 12. Next, the collector layer 11 is etched with a phosphoric acid-based etchant in order to cover the emitter region and the base region with a photoresist and expose the high concentration n-type GaAs layer. Thereafter, using the emitter electrode 19 as the collector electrode 17, an AuGe / Au film composed of a 0.05 μm thick AuGe film and a 0.25 μm thick Au film is formed by a lift-off method, and annealed at 450 ° C. for 5 minutes. Take ohmic junction.

Next, as a base electrode 18, a Ti film, a Pt film, and an Au film, Ti / Pt / Au films each having a thickness of 0.05 μm, 0.01 μm, and 0.15 μm are formed by a lift-off method, and annealed at 300 ° C. for 5 minutes. Perform ohmic junction.

Next, the operation of the bipolar transistor of this embodiment will be described.

In this embodiment, the resistance value per unit area of the resistance layer 14 is about 8 ×
10 ⁻⁶ −Ω1-cm ² . In the bipolar transistor according to the present embodiment, the current density is about 10 ⁻⁵ A / cm ² , so that the voltage drop due to the resistor 14 is about 0.8 V during operation. The temperature coefficient of the resistor formed of the GaAs layer is about 13 × 10
^Since it is ⁻³ / deg, the temperature coefficient of the voltage drop by this resistor is 1.04 mV / deg. On the other hand, the temperature coefficient of the barrier voltage V _BE between the base and the emitter in this embodiment is about −1.0 mV / deg. Therefore, the temperature coefficient of the voltage drop due to this resistor and the temperature coefficient of the base-emitter barrier voltage V _BE have opposite signs, and their absolute values are almost the same, so the positive feedback caused by the increase in collector current due to temperature change Damage can be prevented.

In order to investigate the effect of the present embodiment, as a result of measuring the maximum collector current at which the element is destroyed for the bipolar transistor of the present embodiment and the bipolar transistor without the resistive layer 14, the bipolar transistor without the resistive layer 14 has a collector current of 500 mA. The bipolar transistor of the present example was not destroyed up to about 2 A, while it was destroyed below.

As described above, in the present invention, the resistance for preventing thermal runaway of the bipolar transistor is formed by the semiconductor layer, and the reproducibility of the resistance value is extremely high, and the practical effect is large. is there.

[Brief description of the drawings]

FIG. 1 is a sectional view of a bipolar transistor according to an embodiment of the present invention, and FIG. 2 is a perspective view of a conventional bipolar transistor. 1,11 ... collector layer, 2,12 ... base layer, 3,13 ... emitter layer, 4 ... Ni / Cr ballast resistor, 5,17 collector electrode, 6,18 ... base electrode, 7,19 …… Emitter electrode, 14…
... Low-concentration n-type GaAs layer, 15, 16 ... High-concentration n-type GaAs layer.

Claims (1)

(57) [Claims] A collector layer and an emitter layer are formed on both sides of a base layer, respectively, and have the same conductivity type as the emitter layer on the emitter layer, have a lower impurity concentration than the emitter layer, and A resistor layer having a composition different from that of the emitter layer is formed. A contact layer having the same conductivity type as the resistor layer and a higher impurity concentration than the resistor layer is formed on the resistor layer. A bipolar transistor, wherein an emitter electrode is formed on a layer.