JPS6134273B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for selecting defective optical semiconductor components such as light emitting diodes and semiconductor lasers.

Segregation and abnormal diffusion of impurity atoms in the manufacturing process of optical semiconductor components such as light emitting diodes and semiconductor lasers, such as epitaxial layer growth and diffusion processes,
Defects such as ascending dislocations or defects such as slip dislocations that occur during the pellet mounting process can cause PN in the light emitting part to
Non-light-emitting portions are often generated near the joints. If this has grown sufficiently by the time it reaches the final process of optical semiconductor component manufacturing, problems will occur in the electrical and optical characteristics at the product inspection stage, and defective products with the above defects will be easily sorted out. . However, in optical semiconductor components where the defective portions, i.e., non-emitting portions, are minute and the defects are still growing, no defects appear in normal macroscopic electrical and optical properties such as forward voltage, light emitting output, and light emitting pattern. It is difficult to detect the difference between the product and the normal product, so it is selected as a good product. In such cases, even if the specified function is initially performed without any problems in actual use, the operating current (~several KA/ ^cm2 ) or junction temperature (~200°C) may deteriorate over time.
℃), the above-mentioned non-light-emitting portion becomes apparent, causing failures such as a decrease in light emission output and a stoppage of laser oscillation.

Optical semiconductor components containing the above-mentioned defects must be removed in advance by some means in order to ensure reliability, and various methods have been attempted in this regard since the early days of the appearance of light emitting devices.

For example, the specific resistance or mobility of a crystal substrate has been measured, and substrates exhibiting abnormal values have been rejected as crystallographically imperfect. In addition, we conducted short-term operation tests on finished products and removed those that showed an abnormal decrease in luminous efficiency, as they were judged to have a high risk of shortened lifespan. Further, after completion of manufacturing, all products are subjected to short-time stress operation tests to reveal the above-mentioned defects, and then those with deterioration in electrical and optical characteristics are selected. However, this method not only requires a long time for sorting, but also applies unnecessary stress to non-defective products, which may lead to a decrease in the reliability of non-defective products.

Furthermore, as an improvement over the conventional technology, a steady forward current is applied to the PN junction of an optical semiconductor component, while a pulsed reverse current is superimposed, and the recovery time of excess carrier electrons is measured. There is a method of determining the quality of optical semiconductor components. (T Takahashi 17th Annual Proc.
Reliability Phys Symp P167 (1979)) According to this method, when measuring the reverse recovery time, it is affected by the joint capacitance of the component (object to be measured), so the measured value does not necessarily indicate the presence of defects that have not become apparent. It has the disadvantage that it is not a complete product.

This conceals the fact that the inventor's analytical research shows that there is a close relationship between defects in optical semiconductor components and the lifetime of both bonds with carrier electrons, in terms of measurement technology. ,it is conceivable that.

An object of the present invention is to improve the drawbacks of the above-mentioned prior art and to provide a method that can initially and highly accurately select the quality of optical semiconductor components.

In order to achieve the above object, the present invention applies a high-speed pulse current to an optical semiconductor component, and the delay time of the optical pulse current flowing through a photodetector installed facing the optical semiconductor component via an optical axis alignment jig. This is a method of measuring Below is a brief theoretical explanation:
According to research by the inventors regarding this method, the change in luminous efficiency in optical semiconductor components over time is determined by the radiative recombination lifetime when carrier electrons injected into the PN junction recombine and disappear through the radiative recombination center. ,
It is determined by the change over time of the recombination lifetime, which consists of the non-radiative recombination lifetime when recombination annihilation occurs via non-radiative recombination centers (various defects), and initially the above-mentioned It has become clear that it depends on the defect concentration. As a result, the quality of the optical semiconductor component can be judged by quantitatively knowing the defect concentration or the non-radiative recombination lifetime when the injected carrier electrons recombine and disappear with the defect level.

In such a situation, when the optical semiconductor component is operated with high-speed pulses under low current injection conditions, the input pulse current response characteristic is equal to the non-radiative recombination lifetime (τ _N
The response characteristic of the output optical pulse current is determined by the radiative recombination lifetime ( _τ) , which is slower than the non-radiative recombination lifetime.
_R ) is determined. Therefore, as shown in equation (1) below, an optical pulse current waveform is generated that is delayed by τ _d compared to the input current waveform.

τ _d = τ _R −τ _NR (1) On the other hand, the radiative recombination lifetime τ _R shown in equation (1) has dependence on the injection carrier condition, that is, the pulse current during pulse operation, but generally the change over time is Known not to be seen. However, since the non-radiative recombination lifetime τ _NR depends on the defect concentration shown in equation (2) below, it is affected by changes in the defect concentration over time.

τ _NR (t) ^-1 = τ _NR (o) ^-1 +K・N _T (t) (2) For example, if the injected carrier electrons are all recombined at defects (or deteriorated parts) ) has a large defect concentration, so the non-radiative recombination lifetime τ _NR becomes extremely small, and as a result, the output optical pulse current waveform for measurement is larger than the input pulse current waveform. A delay time will be observed. In addition, (1) (2) above
The symbols for both formulas are as follows.

τ _d : Delay time τ _R : Luminescent recombination lifetime via a radiative recombination center τ _NR : Non-radiative recombination lifetime via a non-radiative recombination center (e.g. defect) N _T : Defect concentration K: Constant Hereinafter, specific examples thereof will be described using the drawings.

FIG. 1 is a block diagram of a delay time measuring circuit for explaining the method of the present invention for selecting defective light emitting diodes. The object to be measured 2 connected to the high-speed pulse generator 1 is connected so that its optical axis coincides with a photodetector 5 whose one end is connected to a high voltage power supply 3 and the other end is connected to a resistor 4 for detecting optical pulse current. They are installed facing each other via a provided optical axis alignment jig 6. Further, a current detector 7 for measuring the pulse current flowing through the object to be measured 2 and a voltage detector 8 connected to both ends of the resistor 4 for detecting the optical pulse current are connected to a sampling oscilloscope 9.

In the measurement circuit of Fig. 1, the object to be measured 2
A pulse current of 100 ns, 1 MHz, 1 mA was applied, and the pulse current waveform (input) and optical pulse current waveform (output) were simultaneously observed with a sampling oscilloscope 9, and the delay time of the latter with respect to the former was measured.

Figure 2 shows the waveform 10 of the pulse current (I _FM ) mentioned above.
FIG. 4 is a diagram showing a waveform 11 of the optical pulse current (I _P ). The latter is temporally delayed by τ _d with respect to the former.

Moreover, FIG. 3 is an example of measurement results showing the current dependence of the delay time (τ _d ). In the same figure, a characteristic curve 12 belongs to a non-defective product, but a characteristic curve 13 belongs to a defective product, and shows a high level of delay time in all current regions. Characteristic curve 1
Although the non-luminescent defective portion of sample No. 3 was not initially clear, another accelerated test confirmed that the defect became apparent in an extremely short time compared to a non-defective product. Therefore, it is clear that defective light emitting diodes can be selected by measuring the delay time of the output light pulse current with respect to the input pulse current in the low current region.

Further, in the above embodiment, a light emitting diode was described, but it is clear from the principle of measurement that a semiconductor laser can be similarly measured.

As mentioned above, when selecting defective optical semiconductor components, there is no need to perform operation tests as in the past, and it is possible to simply measure the delay time of the output optical pulse current with respect to the input pulse current during high-speed pulse operation. Moreover, since the measuring circuit is separated between input and output, it is not affected by the junction capacitance of the object to be measured, and has the effect of being able to quickly and reliably screen out defective products.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the delay time measurement circuit for optical semiconductor components, Figure 2 is a diagram of the observation input pulse current waveform and output optical pulse current waveform of a sampling oscilloscope, and Figure 3 is a diagram of measuring delay time characteristics of optical semiconductor components. This is an example. 1...High-speed pulse generator, 2...Object to be measured, 3
...High voltage power supply, 4...Resistor for optical pulse current detection, 5...Photodetector, 6...Jig for optical axis alignment,
7... Current detector for pulse current measurement, 8... Voltage detector, 9... Sampling oscilloscope.

Claims (1)

[Claims] 1. The light emitting part of the light emitting device and the light receiving part of the photodetector that receives the light are placed facing each other with their optical axes aligned, and the light generated by applying a high speed pulse current to the light emitting device is received by the light receiving part, and the light is detected. A method for selecting light-emitting devices, characterized by measuring the delay time of a light pulse current flowing through the device and comparing it with a certain standard value.