CN104392916A

CN104392916A - Device low-contact-resistivity p-GaN ohmic contact method

Info

Publication number: CN104392916A
Application number: CN201410652524.9A
Authority: CN
Inventors: 李晓静; 赵德刚; 江德生; 刘宗顺; 朱建军; 陈平
Original assignee: Institute of Semiconductors of CAS
Current assignee: Institute of Semiconductors of CAS
Priority date: 2014-11-17
Filing date: 2014-11-17
Publication date: 2015-03-04

Abstract

A device low-contact-resistivity p-GaN ohmic contact method includes the following steps of firstly, preparing a substrate; secondly, growing a low-temperature nucleating layer on the substrate; thirdly, growing an unintentionally-doped GaN layer on the low-temperature nucleating layer; fourthly, growing a moderately-Mg-doped p-GaN layer on the unintentionally-doped GaN layer; fifthly, growing a heavily-doped contact layer on the moderately-Mg-doped p-GaN layer to form a sample; sixthly, conducting Mg activation annealing on the sample; seventhly, processing the surface of the sample, and conducting photoetching on the surface of the sample to form a pattern; eighthly, evaporating an Ni/Au metal layer on the surface of the sample; ninthly, stripping the abundant Ni/Au metal layer; tenthly, conducting annealing alloying on the Ni/Au metal layer to achieve ohmic contact and complete preparation. By means of the method, the performance of the p-GaN ohmic contact can be further improved so that the p-GaN ohmic contact can be applied to GaN-based high-power devices such as blue and green laser devices.

Description

Prepare the method for the p-GaN ohmic contact of low ohmic contact resistance

Technical field

The invention belongs to microelectronics technology, relate to semiconductor material devices manufacturing technology, specifically a kind of method preparing the p-GaN ohmic contact of low ohmic contact resistance.

Background technology

With GaN be the group III-nitride of representative because having a series of superior character, and become one of focus of the research of compound semiconductor in recent years.The features such as its energy gap is large, electronics saturation drift velocity is high, heat conductivility is good are suitable for making high frequency, high-power electronic device; The direct band gap utilizing it wide can make the opto-electronic device of indigo plant, green glow and ultraviolet light.But form high-quality ohmic contact between the manufacture claim metal of GaN base device and semiconductor, for n-GaN, the electrode preparation on it can obtain ohmic contact resistance 10 by Ti/Al system ^-6-10 ^-8Ω cm ²the ohmic contact of scope.And for p-GaN, be difficult to the ohmic contact realizing low ohmic contact resistance, on the one hand due to the p-GaN of very difficult acquisition high hole concentration, be owing to lacking suitable metal system on the other hand.Ni/Au is that current Study of Ohmic Contact selects one of more metal, and be subject to the restriction of the higher activation energy of Mg acceptor, p-GaN doped level is difficult to improve further, therefore how to improve the performance of p-GaN ohmic contact, reduces the emphasis that ohmic contact resistance becomes nitride research.

Summary of the invention

The object of the invention is to propose a kind of method preparing the p-GaN ohmic contact of low ohmic contact resistance, thus improve the performance of p-GaN ohmic contact further, to be applied to GaN base high power device, as blue-green Laser.

The present invention proposes a kind of method preparing the p-GaN ohmic contact of low ohmic contact resistance, comprises the steps:

Step 1: prepare a substrate;

Step 2: at Grown low temperature nucleation layer;

Step 3: grow involuntary doped gan layer on low temperature nucleation layer;

Step 4: the p-GaN layer growing moderate Mg doping in involuntary doped gan layer;

Step 5: grow heavily doped contact layer in the p-GaN layer of medium doped, forms sample;

Step 6: Mg is carried out to sample and activates annealing;

Step 7: processed by sample surfaces, in sample surfaces photoetching, forms figure;

Step 8: at the surface evaporation Ni/Au metal level of sample;

Step 9: unnecessary Ni/Au metal level is peeled off;

Step 10: last Ni/Au metal level carries out annealed alloy, forms ohmic contact, completes preparation.

The invention has the beneficial effects as follows, propose by adopting the present invention using heavily doped p-GaN thin layer and heavily doped p-InGaN thin layer as the method for composite contact layer, the ohmic contact resistance of Ni/Au and p-GaN ohmic contact can be reduced to 4 × 10 ^-5Ω cm ², the p-GaN ohmic contact of this effect can be advantageously applied to and make high-quality high frequency, high power device.

Accompanying drawing explanation

For making the object, technical solutions and advantages of the present invention clearly understand, referring to accompanying drawing, and in conjunction with specific experiment result, the present invention is described in further detail, wherein:

Fig. 1 is growth structure schematic diagram of the present invention;

Fig. 2 is the preparation flow figure of the ohmic contact of the low ohmic contact resistance that the present invention proposes;

Fig. 3 be before improving simple use heavily doped p-GaN cap rock and simple use heavily doped p-InGaN cap rock with improve the rear ohmic contact ohmic contact resistance using compound cap rock to obtain compare distribution map.

Embodiment

Refer to shown in Fig. 1, growth structure of the present invention is followed successively by Sapphire Substrate 01, low temperature nucleation layer 02, involuntary doped gan layer 03, the p-GaN layer 04 of medium doped, heavily doped composite contact layer 05, Ni/Au metal level 06, prepare a method for the p-GaN ohmic contact of low ohmic contact resistance specifically, comprise the steps: as shown in Figure 2

Step 1: prepare Sapphire Substrate 01, this substrate 01 is C surface sapphire, and thickness is generally at 200um to 1000um.Other optional substrates comprise SiC, GaN etc.;

Step 2: growing low temperature nucleating layer 02, its growth is in Sapphire Substrate 01, and low temperature nucleation layer 02 alternate material comprises GaN, AlN etc., and thickness is generally 10nm to 30nm.If substrate selects GaN, then this layer does not need;

Step 3: grow involuntary doped gan layer 03, its growth is on low temperature nucleation layer 02, and the thickness of described involuntary doped gan layer 03 is generally 3-5 μm;

Step 4: the p-GaN layer 04 of growth moderate Mg doping, its growth is in involuntary doped gan layer 03, and described moderate Mg doping p-GaN layer 04 thickness is generally 0.5-3 μm;

Step 5: grow heavily doped contact layer 05, its growth is in the p-GaN layer 04 of medium doped, described heavy doping contact layer 05 comprises heavily doped p-GaN thin layer and heavily doped p-InGaN thin layer, the growth temperature of heavily doped p-GaN thin layer is 800-1100 DEG C, thickness is 10-50nm, heavily doped p-InGaN thin layer growth temperature is 600-800 DEG C, and thickness is about 2-20nm and forms sample.Above five steps is all carry out in MOCVD growth apparatus, is taken out by sample after all completing;

Step 6: Mg is carried out to sample and activates annealing, it is carry out in short annealing furnace apparatus that described Mg activates annealing, under pure nitrogen gas condition, adopt the annealing temperature of 500-800 DEG C to carry out activation annealing, this annealing temperature must be more lower slightly than the growth temperature of heavily doped p-InGaN thin layer, because high temperature can destroy the crystal mass of heavily doped p-InGaN thin layer;

Step 7: sample surfaces is processed, the idiographic flow of sample clean is the ultrasonic 10min of acetone, the ultrasonic 10min of alcohol, hydrochloric ultrasonic wave 10min, in sample surfaces photoetching, forms figure;

Step 8: at the surface evaporation Ni/Au metal level 06 of sample, described Ni/Au metal level is by the evaporation of the method for electron beam evaporation on heavy doping contact layer 05, and the thickness of Ni is the thickness of 10-40nm, Au is 20-80nm.；

Step 9: unnecessary Ni/Au metal level 06 is peeled off;

Step 10: last Ni/Au metal level 06 carries out annealed alloy, and the annealing temperature of described Ni/Au metal level 06 alloying annealing is 450-600 DEG C, and annealing atmosphere is air atmosphere, the ratio of nitrogen and oxygen is 4:1, annealing time is 3-20min, thus forms ohmic contact, completes preparation.

Round coal storage yard method needs to make one group of circular electrode at material surface, and the radius r of each circular metal electrode is identical, is 200 μm.Next circular white space is stayed outside circular metal electrode, and the external diameter R of each annulus reduces gradually, be followed successively by 260,250,240,235,230,225,220,215 μm from big to small, the width d that can obtain annulus is thus respectively 60,50,40,35,30,25,20,15 μm, that is the width d of annulus reduces gradually, is large-area metal outside annulus.It is Keithley 6430 that the sample prepared carries out measuring instrument in test experiments, the both positive and negative polarity that source is shown is connected on respectively the both sides of each annulus, the 8 groups of I-V curves recorded, the linearity of curve obtained is very good, illustrates that the ohmic contact sample of preparation has good ohm property.Measure the resistance Rt between round dot electrode and broad-area electrode separated by annulus, and according to CTLM method, Rt and ln (R/r) is carried out linear fit, through series of computation, the ohmic contact resistance obtained.

The ohmic contact sample that obtains is tested before improving ohmic contact layer and after improving, obtain ohmic contact resistance result as shown in Figure 3, the ohmic contact resistance of the ohmic contact that simple layer is formed is mostly all 10 ^-2, 10 ^-3Ω cm ²within the scope of the order of magnitude, and the ohmic contact resistance that the compound cap rock that we adopt both to combine obtains can reach 4 × 10 very easily ^-5Ω cm ².The ohmic contact of this quality can be applied to GaN base high power device, as blue-green Laser, thus improves the performance parameter of device.

Above-described specific embodiment; object of the present invention, technical scheme and beneficial effect are further described; be understood that; the foregoing is only specific embodiments of the invention; be not limited to the present invention; within the spirit and principles in the present invention all, any amendment made, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims

1. prepare a method for the p-GaN ohmic contact of low ohmic contact resistance, comprise the steps:

Step 1: prepare a substrate;

Step 2: at Grown low temperature nucleation layer;

Step 3: grow involuntary doped gan layer on low temperature nucleation layer;

Step 6: Mg is carried out to sample and activates annealing;

Step 8: at the surface evaporation Ni/Au metal level of sample;

Step 9: unnecessary Ni/Au metal level is peeled off;

2. the method for the p-GaN ohmic contact of the low ohmic contact resistance of preparation according to claim 1, wherein the material of substrate is C surface sapphire, SiC or GaN, and thickness is 200 μm to 1000 μm.

3. the method for the p-GaN ohmic contact of the low ohmic contact resistance of preparation according to claim 1, wherein the material of low temperature nucleation layer comprises GaN or AlN, and thickness is 10nm to 30nm; If substrate selects GaN, then this layer does not need.

4. the method for the p-GaN ohmic contact of the low ohmic contact resistance of preparation according to claim 1, wherein the thickness of involuntary doped gan layer is 3-5 μm.

5. the method for the p-GaN ohmic contact of the low ohmic contact resistance of preparation according to claim 1, wherein the thickness of moderate Mg doping p-GaN layer is 0.5-3 μm.

6. the method for the p-GaN ohmic contact of the low ohmic contact resistance of preparation according to claim 1, wherein heavy doping contact layer comprises heavily doped p-GaN thin layer and heavily doped p-InGaN thin layer, the growth temperature of heavily doped p-GaN thin layer is 800-1100 DEG C, thickness is 10-50nm, heavily doped p-InGaN thin layer growth temperature is 600-800 DEG C, and thickness is 2-20nm.

7. the method for the p-GaN ohmic contact of the low ohmic contact resistance of preparation according to claim 1, wherein Mg activates annealing, under pure nitrogen gas condition, adopt the annealing temperature of 500-800 DEG C to carry out activation annealing, this annealing temperature is lower than the growth temperature of heavily doped p-InGaN thin layer.

8. the method for the p-GaN ohmic contact of the low ohmic contact resistance of preparation according to claim 1, wherein the idiographic flow of sample clean is: the ultrasonic 10min of acetone; The ultrasonic 10min of alcohol; Hydrochloric ultrasonic wave 10min.

9. the method for the p-GaN ohmic contact of the low ohmic contact resistance of preparation according to claim 1, wherein Ni/Au metal level is evaporated by the method for electron beam evaporation, and the thickness of Ni is the thickness of 10-40nm, Au is 20-80nm.

10. the method for the p-GaN ohmic contact of the low ohmic contact resistance of preparation according to claim 1, wherein by Ni/Au metal level annealed alloy, annealing temperature is 450-600 DEG C, and annealing atmosphere is air atmosphere, and annealing time is 3-20min.