technology  gallium oxide


Gallium oxide trumps traditional wide bandgap semiconductors


Transistors built from Ga2O3 have tremendous potential. They have a far higher electric field strength than those made from GaN and SiC,and they can be formed from native substrates produced with simple, low-cost methods, says Masataka Higashiwaki from the National Institute of Information and Communications Technology (NICT), Japan.


T


wo separate developments are needed to secure stable energy supplies in the near future:


Widespread adoption of revolutionary technologies that can replace burning of fossil fuels; and the introduction of a multitude of products that consume less energy, a step that will also trim greenhouse gas emissions.


One way to fulfil this latter goal is to turn to more efficient power electronics. This is possible by replacing silicon devices with those made from wide bandgap semiconductors, which have superior material properties, such as higher breakdown voltages and lower switching losses.


The two most promising, highly developed wide bandgap materials for power electronics are GaN and SiC. However, both of them have massive weaknesses when it comes to mass production. In an ideal world, compound semiconductor devices are built on an affordable native substrate, but it is impossible to make GaN and SiC crystals with simple, low-cost methods. Current methods to make GaN lead to sale prices that


are prohibitively high for power electronics, and while SiC substrates don’t suffer from the same fate, they are still costly and their material quality is far from perfect.


A promising wide bandgap alternative that has been overlooked up until now is Ga2


O3 . Thanks to a bandgap


that is significantly larger than that of SiC and GaN, this oxide promises to enable the production of devices with higher breakdown voltages and higher efficiencies than those stemming from its wide bandgap rivals. What’s more, Ga2


O3


power devices could be manufactured at low cost in high volume, because it is possible to produce single-crystal native substrates from a melt using the same method employed for manufacturing sapphire substrates. This platform for making GaN LEDs is now being manufactured in a low-cost commercial process in numbers rivaling those for silicon substrates; there is no major obstacle to prevent Ga2


O3


from treading the same path. To try and convert the promise of Ga2


O3 substrates power devices


into a reality, since 2010 I have been working in collaboration with Kyoto University, the Tokyo Institute of Technology, and Tamura and Koha Corporations. Our team has already developed several elemental technologies and hit several key milestones, including the world’s first demonstration of Ga2


O3 O3 transistors.


The character of gallium oxide Ga2


O3


has many forms, and to date there have been confirmed reports of five different polytypes, which are denoted α, β, γ, δ and ε. The β-polytype is the most stable, and the four other polytypes are classed as quasi-stable. Since efforts on Ga2


Table 1.In terms of break down field and Baliga’s figure of merit, Ga2


O3 is superior to all the popular compound semiconductor materials 20 www.compoundsemiconductor.net June 2012


are in their infancy,


there have only been a handful of reports on crystal growth and material properties of this oxide, and they have focused on the β-phase. This polytype has several attractive attributes, including an incredibly wide


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105